astro-ph.GA

Top Pith

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astro-ph.GA 2026-06-24

Barred spiral galaxy found at z=5.102

by Xiaohan Wang, Fengwu Sun +22 more

A massive barred spiral galaxy at z = 5.102 discovered by JWST

JWST imaging reveals a 4.5 kpc stellar bar and spiral arms in a massive disk galaxy only 1.2 billion years after the Big Bang.

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We report M1149-BSG-z5, a barred spiral galaxy at $z = 5.102$, identified in the parallel field of MACS J1149+2223 with JWST and HST. M1149-BSG-z5 is the highest redshift barred galaxy candidate to date. Both isophote ellipse fitting and structural modeling support a stellar bar of length $a_\mathrm{bar} \approx 4.5$ kpc, and extended spiral arms peaking at $r \approx 5.5$ kpc. M1149-BSG-z5 is a massive main sequence star-forming galaxy, with a stellar mass of $10^{10.45}\rm M_\odot$ and a star-formation rate of $144\,\rm M_\odot/yr$. A concentrated bulge is embedded in an extended disk with a global S\'ersic index $n = 2.37$. With an effective radius of $R_{e} = 2.61\rm \ kpc$, M1149-BSG-z5 is larger than typical galaxies at $z \sim 5$ and comparable to barred galaxies at $2 < z < 4$. M1149-BSG-z5 also hosts a broad-line AGN, with a relatively low black-hole-to-stellar mass ratio of $\rm M_{\rm BH}/M_\ast\sim10^{-3}$. Its metal-enriched emission-line properties indicate that it is already chemically evolved. These properties imply M1149-BSG-z5 as an early-assembled and structurally evolved galaxy. We also find that M1149-BSG-z5 resides in an overdense region with a nearby companion galaxy, suggesting an interaction-driven bar formation mechanism. Its concentrated light, early assembly and main-sequence star formation also suggest baryon-dominated, gas-rich conditions, where gravitational instability can further accelerate the bar formation.

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astro-ph.GA 2026-05-22 2 theorems

This paper reports a mean velocity difference of about 0.05 km/s between ions traced by…

by Doris Arzoumanian, Silvia Spezzano +10 more

Probing the ion-neutral drift velocity towards the L1544 prestellar core: Detection of ambipolar diffusion using N₂D^+ and para-NH₂D

Detection of ~0.05 km/s ion-neutral velocity drift in L1544 interpreted as the first observational signature of ambipolar diffusion in a…

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The dynamical role of the magnetic field in the star formation process is tightly linked to the coupling between matter and the field. This coupling is due to the interaction between ions and neutrals in the partially ionized interstellar medium. When the ionization degree drops in the dense environment of prestellar cores, the magnetic field and the matter may decouple, leading to differences in the infalling velocities of ions and neutrals known as ambipolar diffusion. The onset of gravitational collapse resulting from ion-neutral decoupling has never been observed. The aim of this work is to search for signatures of ambipolar diffusion within a prestellar core. We observed the deuterated N$_2$D$^+$ ion and the neutral para-NH$_2$D species towards the prototypical prestellar core L1544. These two species are ideal tracers of prestellar cores sampling the same high densities in the core interior. We compared the velocity centroid and linewidth maps of the ion-neutral pair. We find a mean ion-neutral velocity difference of $\sim$0.05 km/s towards the core. By comparing with predictions from self-consistent calculations of the ambipolar resistivity including dust grain growth, we interpret the observed ion-neutral velocity difference in L1544 as a signature of ambipolar diffusion. We do not detect a significant ion-neutral linewidth difference that may be attributed to the subsonic infall motions of the gas in L1544 and geometrical effects in the presence of inclination. These results emphasize the role of dust grain growth at the prestellar core stage in setting the ambipolar resistivity and regulating the dynamical evolution of dense cores towards their collapse into protostars. We propose that measurements of ion-neutral drift velocities provide new constraints on the total magnetic field strength and the dust size distribution within prestellar cores.

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astro-ph.CO 2026-05-20 2 theorems

Photometric data alone yields first splashback mass function for clusters

by Lucas Gabriel-Silva, Laerte Sodré Jr

The Splashback Mass Function of Galaxy Clusters from Photometric Data

SDSS photometry locates cluster edges and produces abundances matching simulations at high masses.

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The splashback radius marks the physical boundary of galaxy clusters, separating orbiting from infalling material, and provides a halo definition free from pseudo-evolution. In this work, we present a fully photometric framework to measure individual cluster splashback radii and masses, and to construct an observational splashback mass function. Using Sloan Digital Sky Survey data, we develop a probabilistic cluster membership method based on radial and photometric redshift information, optimized through an adaptive probability cut that maximizes the detection significance of the cluster core relative to its outskirts. We apply this methodology to a sample of 499 galaxy clusters from the \textsc{CoMaLit} weak-lensing compilation and recover splashback radii from modeling cumulative galaxy number profiles. The resulting splashback radii exhibit a median ratio $R_{\mathrm{sp}}/R_{200\mathrm{m}} \simeq 1.1$, consistent with previous observational studies. Using these measurements, we recalibrate the $M_{\mathrm{sp}}$--$R_{\mathrm{sp}}$ scaling relation over a wide redshift range ($0.01 < z < 0.8$), finding a slope shallower than the constant-density expectation and no significant redshift evolution. We then apply this relation to \textsc{redMaPPer} clusters in the SDSS Northern Galactic Cap to derive splashback masses for more than $1.5\times10^4$ systems and construct the first observational splashback mass function based solely on photometric data. The resulting mass function agrees with simulation-based predictions at the high-mass end, while deviations at lower masses are consistent with known completeness limits of optical cluster catalogs. Our results demonstrate that splashback-based cluster sizes, masses, and abundances can be robustly measured in photometric surveys, enabling cosmological studies without spectroscopic or lensing data.

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astro-ph.GA 2026-07-03

Merger stretches Andromeda disc beyond 40 kpc

by C. Tsakonas, M. Arnaboldi +5 more

The Merger-Driven Origin of the Vast Extended Stellar Disc Around the Andromeda Galaxy

N-body model shows 2-4 Gyr event heats and warps the progenitor disc with inclination falling at larger radii

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The closest giant spiral, the Andromeda galaxy (M31), shows compelling evidence for a recent, gas-rich major merger event. Pronounced substructures in its inner halo and a kinematically hot stellar disc, whose star formation history shows a widespread star formation episode 2.5 Gyr ago, are telltale evidence that may be directly linked to a major (mass ratio 1 to 4) merger event that took place 2-4 Gyr ago. Spectroscopy of resolved giant stars in the remote outskirts of M31's disc revealed a vast extended structure that rotates with a circular velocity close to the HI gas. In addition, the spatial distribution and significant prograde rotation of two distinct, compact groups of globular clusters (GCs) in the disc outskirts are unusual for typical inner halo GCs. We employ an available N-body hydrodynamical simulation of a major merger that reproduces the morphology of the inner halo substructures, the age-velocity dispersion relation, and the star formation history in the disc. We compare model particles with resolved tracers in the M31 disc. To examine the evolution of the progenitor M31 disc -- that appears to get stretched, distorted, and warped due to the gravitational perturbation inflicted by the major merger -- we investigate the properties of the pre- versus post-merger discs of the simulated analog. The merger transforms the disc of the progenitor galaxy, which becomes kinematically hot and asymmetric. In addition, the post-merger disc gets stretched by almost a factor of 2, and its extent spans distances greater than 40 kpc. The stellar warp in populations older than 2 Gyr is characterized by a monotonic decrease of inclination with radius, with the outer stellar distribution appearing less edge-on at larger galactic radii. These results provide a comprehensive picture of the evolution of the giant disc of M31, the closest merger-inflicted massive galaxy.

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astro-ph.GA 2026-07-03

SKAO spectra will uncover the first radio AGN in the epoch of reionization

by Jose Afonso, Stergios Amarantidis +21 more

The Road to Identifying the Earliest Radio-Powerful AGN with the SKA

Fine sampling from 50 MHz to 15 GHz overcomes biases that hide the predicted population of early radio-powerful sources.

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The Epoch of Reionization (EoR) is one of the most pivotal frontiers in modern astrophysics, marking the emergence of the first galaxies, stars, and supermassive black holes (SMBHs). Despite insights from the Atacama Large Millimetre/submillimetre Array and the James Webb Space Telescope, we still struggle to explain how $\sim10^{9}$ M$_\odot$ SMBHs powering luminous active galactic nuclei (AGN) already exist by $z\sim7$. The recent discovery of powerful radio emission from some of these early AGN is notable, offering new constraints on early black-hole accretion and, with the Square Kilometre Array Observatory (SKAO), the prospect of directly probing neutral hydrogen through 21-cm absorption studies. Yet progress remains slow: only a few radio-powerful AGN are known at $z>6$, far fewer than theoretical predictions suggest, raising questions about whether this reflects intrinsic properties or selection biases and incomplete spectral information. In this chapter we synthesise predictions from state-of-the-art hydrodynamical and semi-analytic simulations with observational constraints from SKAO pathfinder facilities. These models suggest the existence of a substantial, still-undetected population of radio-powerful AGN in the EoR, but show that present surveys are limited by selection biases and incomplete radio spectral information. We discuss a physically motivated strategy for identifying high-redshift radio AGN, based on broadband radio spectral energy distributions, spectral curvature, dynamical jet evolution, and radio-only redshift estimation, offering a transformative alternative to traditional empirical approaches. Finally, we justify how the sensitivity and spectral coverage of the SKAO will allow fine-frequency sampling across the 50 MHz - 15 GHz range, revolutionising our ability to identify the earliest radio-powerful AGN and probe the earliest SMBHs.

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astro-ph.GA 2026-07-03

Code shows dwarf-star contamination peaks near survey limits

by Onnalin Innala, Nicha Leethochawalit +2 more

Assessing Ultra-Cool Dwarf Contamination in Photometrically Selected High-Redshift Galaxy Samples

FC-ENZO finds similar fractions across HST, Roman and JWST fields but most interlopers sit at the faintest magnitudes.

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Ultra-cool dwarf stars (UCDs) are a common source of contamination in high-redshift galaxy searches as both sources are red and these early-forming galaxies can have sizes that are difficult to resolve even with space telescopes. Standard selection techniques, including photometric redshift estimation and color-color criteria, cannot fully eliminate this contamination. We develop \textbf{F}oreground \textbf{C}ontamination \textbf{E}valuator of \textbf{N}earby dwarf stars in high-\textbf{Z} photometrically selected \textbf{O}bjects (FC-ENZO), a code that predicts the number of dwarf stars misidentified as high-redshift galaxies for a given survey setup. FC-ENZO models the number of UCDs and evaluates the fraction of synthesized dwarf stars that passes user-specified selection methods. We compare two synthetic spectral energy distribution libraries and find that the ELF OWL library, which relaxes the assumption of chemical equilibrium, predicts larger contaminant fractions than the BOBCAT library, because of stronger absorption features around $ 1 $ \micron. The contamination fraction increases with metallicity and also depends on the adopted stellar number-density model. The dominant contaminants are T to early Y-type UCDs, which are most commonly misclassified as galaxies at $z \sim 8$. Comparing deep surveys from different space telescopes, we find similar overall contamination levels within the same redshift range. However, the contamination is concentrated near the limiting magnitude of each survey. At brighter magnitudes, the relative contamination is highest for HST (COSMOS), followed by Roman deep-tier survey, and JWST. Although the predicted contaminant numbers remain sensitive to model assumptions, FC-ENZO provides a practical tool for survey design and for identifying optimal fields for spectroscopic follow-up.

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astro-ph.GA 2026-07-03

Grain growth starts before collapse in forming cores

by E. Zhu, I. Ristorcelli +6 more

Tracing grain growth in the forming prestellar core L1506C with 3D modeling of Herschel, IRAM, and CFHT observations

L1506C modeling shows evolved dust grains are needed in densest regions, implying early evolution in star formation.

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In the early phases of star formation, properties of prestellar cores are commonly inferred from observations of thermal dust emission and thus depend on dust properties, which must be carefully characterized. Our target, L1506C, is part of the filament L1506 in the Taurus molecular cloud. The spectral energy distributions over the whole spectral range (from 160 {\mu}m to 2 mm), built from Herschel PACS and SPIRE and IRAM-NIKA2 data, have been fitted with a modified blackbody. These data were also modelled using the 3D radiative transfer code SOC and the latest THEMIS 2 dust model using extinction observations from WIRCam at CFHT and from Spitzer as additional constraints. The MBB modeling reveals that L1506C is fragmented into two low density cores with masses smaller than their Jeans masses. The dust color temperature and the emissivity spectral index show clear anti-correlation and change in grain properties. Grains more evolved than the diffuse interstellar medium are needed to model the densest part showing that grain growth already occurs at very early stage of star formation, even before the onset of gravitational collapse.

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astro-ph.GA 2026-07-03

GCs form at 3 million solar masses per enrichment stage

by Irina Acharova, Margarita Sharina

Indicatives of Early Stages of Star Formation in the Universe

Four matching metallicity peaks in clusters and clouds from z=0.2 to 5.9 are reproduced when each stage produces that fixed GC mass total.

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The paper analyzes formation conditions for globular clusters (GCs) in circumgalactic clouds. The similarity between the metallicity distributions of GCs in the nearby Universe and of circumgalactic clouds is substantiated in detail over a wide range of redshifts: from \mbox{0.2} to \mbox{5.9}. The distributions of the number of circumgalactic clouds and GCs both contain a sequence of four local maxima at the metallicity values: \mbox{$[\rm{X/H}]\simeq -2.6, -2.0, -1.4,-0.5$}. The sequential enrichment of a circumgalactic cloud with a mass of $10^{8}\,M_{\odot}$ is calculated starting the extremely low metallicity \mbox{$ [\rm{X/H}] <-2.3$}, then following through the stages of \mbox{$-2.3 \le [\rm{X/H}]<-1.7$} and \mbox{$-1.7 \le [\rm{X/H}] < -0.9$} to the high metallicity \mbox{$[\rm{X/H}] \ge -0.9$}, where the boundaries of these ranges coincide with the local minima of the number of objects in the distributions. It is shown that for the reproduction of such distributions, it is sufficient that at each stage of enrichment of a part of a cloud in metals, one or more GCs with a total mass of \mbox{$3 \times 10^{6}\,M_{\odot}$} are formed. It is shown that the maximum mass of stars capable of leading to supernova explosions increases with the increase of metallicity. Possible values of this mass are calculated for the metallicities corresponding to the maxima in the distributions of clouds and GCs.

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astro-ph.GA 2026-07-03

3 GHz survey finds 65 polarised sources but zero star-forming galaxies

by S. Ranchod, S. A. Mao +6 more

The VLA-COSMOS 3 GHz Large Project: Polarised source counts and catalogue

Upper limit below 2 per square degree shows SKA-era work needs far deeper data to detect this population.

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The exploration of the faint polarised radio source population is essential for interpreting the nature and evolution of magnetic fields in galaxies. While recent studies have provided insight into source counts for the $\mu$Jy polarised source population at 1.4 GHz, higher frequency surveys may be more sensitive to new populations that are depolarised at lower frequencies (i.e. due to internal or external depolarisation effects). We present the deepest polarised source counts at 3 GHz to date, at an angular resolution of $1.5''$. With these relatively higher frequency observations, we aim to probe the faint polarised star-forming galaxy (SFG) population. Furthermore, through spectral modelling, we aim to provide further insight into the frequency evolution of polarised source counts. We processed the polarisation data of the VLA-COSMOS 3 GHz Large Project, one of the deepest high-resolution radio continuum surveys. We produced Stokes Q and U mosaicked channel maps. After selecting known sources in total intensity, we performed 3D rotation measure synthesis and searched for polarised emission using an empirically determined threshold. With a sensitivity of 2.6 $\mu$Jy/beam in Faraday depth, we detect 65 polarised sources (51 deg$^{-2}$) above our threshold. We find that our cumulative and Euclidean-normalised source counts at 3 GHz are consistent with those in the literature at 1.4 GHz, which we attribute to the combined effect of spectral index and depolarisation in the detected sources. We detect no SFGs in our sample and derive a 2$\sigma$ upper limit on the density of polarised SFGs of $<2.0~\mathrm{deg}^{-2}$. This implies that significantly deeper observations will be required to readily detect this population in the SKA-era.

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astro-ph.GA 2026-07-03

SKA-mid AA4 to deliver resolved HI maps over hundreds of square degrees

by M. Ramatsoku, P. Serra +9 more

Resolved HI and Environmental Dynamics

Reaching 10^18 cm^{-2} sensitivity at kiloparsec scales across clusters, groups and filaments.

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Spatially resolved, deep HI observations from SKA precursors and pathfinders such as MeerKAT, FAST, and ASKAP have demonstrated their ability to reveal the complex interactions between galaxies and their environments. These include, but are not limited to, recent observations of the Virgo cluster showing that the hydrodynamical effects of ram pressure stripping can operate effectively at unexpectedly large cluster-centric distances. In the Fornax cluster, the discovery of long HI tails with mixed tidal-ram-pressure origins indicates the interplay between gravitational and hydrodynamical mechanisms. Similar HI features in nearby filaments and galaxy groups, where ram pressure is expected to be weak, highlight the influence of hydrodynamical processes even in low-density environments. Multi-resolution studies have further revealed signs of cold gas accretion and HI replenishment driven by tidal interactions. While highly informative, these studies remain limited to small, specific regions of the sky. With SKA-mid AA4, it will become possible to carry out deep, spatially resolved HI imaging over hundreds of square degrees, covering environments from isolated galaxies to filaments. By reaching column-density sensitivities between $1.0 \times 10^{18}$ and $\sim 1.0 \times 10^{19}~\mathrm{cm^{-2}}$ at physical resolutions of $\sim$10 and $\sim$1 - 2 kpc, respectively, and by enabling sensitive, contiguous observations of wide areas within short integrations, SKA-mid AA4 will allow the construction of large, statistically representative samples of galaxies and detailed studies of environmental mechanisms operating across the full range of these less-studied environments at resolved scales.

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astro-ph.GA 2026-07-03

Nine southern supernova remnants receive new distance measurements

by Fupeng Liu, He Zhao +3 more

Distance Determination of Southern Galactic Plane Supernova Remnants with the Mopra CO Survey and DECaPS 3D Dust Map

CO clouds and 3D dust maps yield distances accurate to roughly 5-10 percent for objects in the galactic plane.

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Accurate distance measurements to supernova remnants (SNRs) are crucial for understanding their physical properties, evolutionary processes, and role in the Galactic interstellar medium (ISM) cycle. In this study, we apply for the first time to the southern Galactic plane a distance determination method that utilizes CO emission data from the Mopra survey to identify molecular clouds (MCs) interacting with SNRs. By combining this with extinction-distance profiles from the DECaPS three-dimensional (3D) extinction map, we directly measure the distances to the associated MCs, thereby obtaining precise distances to the remnants. To overcome the extinction-missing bias in extremely dense regions where the 3D map suffers from a deficit of background stars, we supplement our analysis with two-dimensional (2D) extinction maps as cross-validation. Applying this method, we have derived precise distances for nine SNRs: G290.1-0.8 (7.32+0.60/-0.47 kpc), G292.2-0.5 (10.85+0.43/-0.68 kpc), G296.1-0.5 (4.59+0.18/-0.19 kpc), G296.8-0.3 (8.74+0.40/-0.29 kpc), G298.6-0.0 (6.50 +/- 0.21 kpc), G312.4-0.4 (3.60+0.19/-0.23 kpc), G332.4-0.4 (2.66+0.23/-0.15 kpc), G335.2+0.1 (2.76+0.37/-0.31 kpc), and G353.6-0.7 (1.81+0.18/-0.14 kpc). Additionally, we established a robust lower distance limit of 1.34 kpc for G351.7+0.8.

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astro-ph.EP 2026-07-03

TESS detects first bound microlensing planet

by Mallory Harris (University of New Mexico), Diana Dragomir (University of New Mexico) +3 more

TESS's First Bound Microlensing Planet: A Binary Microlensing Event Revealing a Planetary Companion toward the Galactic Plane

Combined photometry shows a 1.6 Jupiter-mass planet around a K dwarf at 4.8 AU projected separation along the Galactic plane.

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We report the discovery of Gaia23bra b, the first gravitationally bound microlensing planet detected by the Transiting Exoplanet Survey Satellite (TESS). Initially flagged as a single-lens event by the Gaia Science Alerts system, Gaia23bra was serendipitously observed by TESS over two consecutive sectors. During those TESS sectors, the light curve of the event displayed caustic-crossing features characteristic of a binary-lens event. Joint modeling of Gaia and TESS photometry with pyLIMA, supplemented by stellar parameter inference using pyLIMASS, suggests a K dwarf ($M_L = 0.79^{+0.19}_{-0.17}\,M_\odot$) hosting a Jovian planet with $M_P = 1.63_{-0.38}^{+0.42}\,M_{\rm Jup}$ at a projected separation of $a_{\perp,\min} \approx 4.8\,\mathrm{AU}$. This result underscores the synergy between high-cadence photometry and long-baseline monitoring for robust microlensing characterization. Its location along the Galactic Plane highlights TESS's unexpected capacity for microlensing science through its all-sky coverage and its potential to detect planets in regions beyond the Galactic Bulge.

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astro-ph.GA 2026-07-03

Ring post-starburst galaxies evolve into AGN hosts

by Junjie Huang, Yanmei Chen +8 more

Post-starburst Galaxies with Active Galactic Nucleus: Properties and Evolutionary Sequences

Age and kinematic profiles link RPSBs to later AGN activity while high-mass central PSBs follow mergers; AGN feedback is not required for qu

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Post-starburst (PSB) galaxies, identified by strong Balmer absorption and weak nebular emission, provide a key laboratory for studying rapid quenching. Using the final data release of the SDSS-IV MaNGA survey, we follow the traditional PSB selection criteria of Chen et al. (2019) and develop a new method to identify regions that simultaneously exhibit PSB features and nuclear activities (AGN-PSBs). Our final sample comprises 48 AGN-PSBs, 92 central PSBs (CPSBs), 89 ring-like PSBs (RPSBs), and 828 irregular PSBs (IPSBs). We find the global and spatially resolved properties of CPSBs and RPSBs are consistent with the results of Chen et al. (2019). In this work, we focus on the properties of AGN-PSBs, comparing them with CPSBs, RPSBs, and control galaxies. Similar to CPSBs and RPSBs, AGN-PSBs show positive $\mathrm{D}_{n}4000$ gradients relative to negative $\mathrm{D}_{n}4000$ gradients of their controls, which indicates younger stellar populations in the central region than that in the outskirt. Among the three sub-types, high-mass CPSBs (H-CPSBs, with $\log(M_{*}/M_{\odot})>9.5$) display the highest incidence of merger remnants and gas--star kinematic misalignment, consistent with a merger/interaction-dominated origin. AGN-PSBs and RPSBs, however, show lower and comparable fractions of merger remnants and gas--star kinematic misalignment, favoring less violent external mechanisms. Based on radial profiles of mass-weighted age and $V_{\rm star}/\sigma_{\rm star}$, we suggest that RPSBs can evolve into AGN-PSBs, whereas H-CPSBs likely follow a distinct evolutionary pathway. The existence of RPSBs and IPSBs also indicates that AGN feedback is not a necessary condition for the formation of PSB.

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astro-ph.IM 2026-07-03

No periodic radio signals detected from 3I/ATLAS

by Jian-Kang Li, Zhen-Zhao Tao +2 more

Periodic Radio Technosignature Search toward 3I/ATLAS with FAST

FAST telescope search using signal decomposition sets upper limit of 0.146 watts on artificial periodic emissions

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3I/ATLAS, the third confirmed interstellar object discovered in the Solar System, provides a unique opportunity for targeted technosignature searches. We report a periodic radio technosignature search toward 3I/ATLAS using the Five-hundred-meter Aperture Spherical Telescope (FAST) L-band multibeam receiver. To search for periodically modulated signals and distinguish center-beam-dominated candidates from multibeam radio-frequency interference, we apply canonical polyadic decomposition (CPD) to the multibeam dynamic spectra. CPD factorizes the multibeam data tensor into a set of separable components, with associated time, frequency, and beam signatures. Candidate components are then selected through periodogram and autocorrelation diagnostics. We find no credible artificial periodic radio technosignature above 0.146 W is detected from the direction of 3I/ATLAS. This search expands the range of signal types explored for this target by including periodic modulated signal, and illustrates that CPD is a promising framework for multibeam periodic technosignature searches.

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astro-ph.GA 2026-07-02

Filtering creates a window for broad lines across AGN accretion rates

by Mohammad Hassan Naddaf

Radiative filtering unifies broad-line phenomenology in active galactic nuclei

The product of intrinsic ionizing output and transmission explains why lines vanish at both low and high accretion and unifies multiple obse

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Broad emission lines (BELs) are a defining feature of active galactic nuclei (AGNs), yet they weaken or disappear in both very low- and very high-accretion systems. These regimes are typically treated separately, and a unified physical explanation has remained elusive. Here we show that this behavior arises if line formation is governed not by the intrinsic luminosity of the central engine, but by the ionizing radiation field that survives filtering before reaching the broad-line region (BLR). In this picture, line production depends on the product of intrinsic ionizing capability and an effective transmission. Because the former increases from low accretion rates while the latter declines at high accretion rates, the effective ionizing field naturally develops a finite and non-universal window for BEL formation. This framework unifies the absence or extreme faintness of BELs in low-luminosity AGNs, LINERs, and weak-line quasars (WLQs), and accounts for the Baldwin effect and the $R_{\rm Fe}$ trend. It also necessarily implies the breakdown of standard BLR-based scaling relations in extreme accretion regimes. We show that a minimal quantitative realization reproduces this behavior across black-hole mass, accretion rate, and radiative efficiency. These results suggest that AGN emission-line phenomenology is governed by global regulation of the ionizing radiation field rather than by mere presence or condition of local gas.

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astro-ph.GA 2026-07-02

Variable dimension fits Milky Way curves without dark matter

by Gabriele U. Varieschi

Fractional-Dimension Gravity and the Milky Way Galaxy

A radially changing fractional space dimension matches Gaia DR3 velocities across the full observed range.

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In this work, we focus our analysis of Fractional-Dimension Gravity (FDG) on our home galaxy, the Milky Way (MW), by using the latest Gaia DR3 data as well as previous rotation curve (RC) data for this galaxy. FDG is an alternative gravitational model (previously known as Newtonian Fractional-Dimension Gravity - NFDG) which does not require the dark matter (DM) paradigm. The MW is studied here with the methods of FDG and its observed rotation curves are successfully reproduced by using a variable fractional dimension $D\left (R\right)$, following previous studies of several other galaxies which were analyzed with the same methodology. An alternative dimension function $D_{m}\left(R \right)$, based on the mass-dimension field equation, was also used and yielded less accurate fits to the experimental data. In addition, we also considered possible implications of the FDG metric, based on the presence of additional weights, on the structure of Special Relativity (SR) for spacetimes with fractional dimension. One notable outcome of this analysis is the possibility of an effective superluminal motion in galactic regions where the space dimension is $D<3$. Although this result is very speculative, it opens interesting new perspectives for possible interstellar travel in our galaxy.

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astro-ph.GA 2026-07-02

Neural net turns edge-on galactic center data into top-down maps

by B. L. DuBois, Cara Battersby +12 more

IRIS: Deciphering Spectral-Line Imagery of the Galactic Center by Machine-Learning on Simulations

Trained only on simulations, the model produces new projections of the Central Molecular Zone from SEDIGISM observations.

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In understanding the 3D structure of the Milky Way's Central Molecular Zone (CMZ), we are limited by our edge-on perspective. Towards addressing this problem, we introduce Imagery Reversion Informed by Simulation (IRIS). IRIS is a novel machine-learning code base featuring a deep convolutional neural network (CNN), which we have designed to translate edge-on observations of our Milky Way Galaxy into top-down images by training on data generated from AREPO galaxy simulations and synthetic observations of those simulations. We develop a large custom dataset on which we train our bespoke model, and then test the trained model on synthetic data to probe the potential of this machine-learning method, which we call supervised reversion. We then apply our trained model to real observations from the SEDIGISM 13CO(2-1) survey, yielding new top-down views of our CMZ. Though our SEDIGISM reversions are not fully consistent across model training runs, we posit that this lack of convergence can be alleviated by expansion of the training dataset. We argue that these results represent a strong proof-of-concept for the use of supervised reversion to decipher our CMZ's 3D structure. Crucial in generating our training dataset's 100k synthetic observations, we introduce IRIS Synthetic Observation (IRIS-SO), a new GPU-accelerated and fully differentiable code implemented in PyTorch for the non-LTE synthetic observation of spectral lines and dust. We find that IRIS-SO provides up to 10,000x speedups in comparison to the synthetic-observation code RADMC-3D. We release all the IRIS code open-source at https://github.com/bldubois/IRIS.

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astro-ph.GA 2026-07-02

Primordial segregation shapes denser cluster tidal tails

by S. Mojtaba Ghasemi, Hosein Haghi +4 more

The fingerprint of primordial mass segregation on the tidal tails of star clusters

Simulations show segregated clusters form longer, unified tails early on, with the signal weakening at later times.

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We investigate the effect of primordial mass segregation (PMS) in shaping the tidal tail structures of star clusters, searching for any trace of PMS on the tails at both early and late evolutionary stages. Through N-body simulations, we analyze clusters with two different degrees of PMS at various Galactocentric distances (R_G), considering two black hole retention scenarios. Our findings reveal that PMS influences early cluster expansion and the formation of tidal tails with a bottom-heavy stellar mass function, this being more pronounced at smaller R_G but diminishes over time. Primordially segregated clusters exhibit denser, unified, and longer tail structures compared to non-segregated clusters. The mean stellar mass distribution along the tails shows distinct patterns for primordially segregated and non-segregated clusters, converging at later evolutionary stages. The retention of stellar remnants has a weak impact on the mean mass distribution along the tails and on its morphology. We find that although mean mass differences persist along the tidal tails, the rate of change in primordially mass-segregated clusters eventually converges with that of non-segregated clusters, suggesting that the influence of primordial mass segregation on the tidal tails gradually diminishes over the course of cluster evolution.

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astro-ph.GA 2026-07-02

Extreme outflows mark quasars shedding dust cocoons

by Guozhen Ma, Stefan J. Geier +12 more

Extreme outflow velocities and weak UV emission lines indicate quasars shedding their dust cocoons

Six objects with 0.16c blueshifted BALs and weak UV lines fit low-inclination disc winds where dust shatters during emergence.

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The recently discovered low-ionisation broad absorption line (LoBAL) quasar GQ 1309$+$2904 is unusual due to its very broad, highly blueshifted absorption troughs and an absence of broad emission lines except for ${\mathrm{H} \alpha}$. In this paper, we present observations of six quasars that appear very similar to GQ 1309$+$2904 in the rest-frame ultraviolet (UV). We measure the systemic redshifts of these quasars to be $z\approx$ 2.07--3.28 from detected ${\mathrm{H} \alpha}$ emission lines. We confirm that all targets are quasars with highly blueshifted BALs possessing high-speed outflows with velocities up to $\sim 0.16\,c$, and five of them are confidently identified as LoBAL quasars. Based on ${\mathrm{H} \alpha}$ emission, black hole masses and Eddington ratios of these quasars are $M_{\mathrm{BH}} \approx 10^{8.7}$--$10^{9.4}\,M_{\odot}$ and $L_{\mathrm{bol}} / L_{\mathrm{Edd}} \approx$ 0.14--0.34, indicating that their central black holes are very massive and active. Every quasar in our sample exhibits a very flat or reddened continuum. The spectral shapes of three objects are well-fitted by a normal quasar composite reddened by a Small-Magellanic-Cloud-like (SMC-like) extinction curve, while the other three require a steeper extinction law. Broad-band ($BVR$) polarimetry for two of the latter group (plus GQ 1309$+$2904) reveals their low polarisations, consistent with low inclination (more face-on) angles. We propose that these objects are weak emission-line quasars (WLQs) observed through the disc wind, caught emerging from their dust cocoons. As quasars shed their cocoons, dust grains in the disc wind are shattered into smaller particles, producing the UV-steeper extinction curve observed along the outflow. We present a schematic illustration of this shedding process that can account for the peculiar spectral features observed in our sample.

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physics.flu-dyn 2026-07-02

Collapse flow adds no vorticity to irrotational turbulence

by Axel Brandenburg, Evangelia Ntormousi +1 more

No evidence of vorticity production from initially irrotational turbulent gravitational collapse

Simulations show all vorticity traces to initial conditions, with none generated by the gravitational collapse itself.

abstract click to expand

Gravitational collapse creates large amounts of kinetic energy that could potentially seed turbulence. If such turbulence were also suitable to initiate dynamo action, the resulting magnetic field would further modify the dynamics, especially on small length scales. However, a small-scale dynamo requires vortical turbulence, while the collapse produces mainly irrotational motions, which may not be efficient for dynamo action. Here, we study the efficiency of vorticity production during a turbulent collapse. We use a barotropic equation of state, where pressure and density gradients are parallel, and no magnetic field, so that vorticity can only be produced by viscosity. Using direct numerical simulations of gravitational collapse, we show that, for the parameter space accessible to our numerical resolution, this effect is related to the initial irrotational turbulence and is not a consequence of the collapse flow.

0

astro-ph.CO 2026-07-02

SPT-3G survey yields catalog of 7190 confirmed galaxy clusters

by L. E. Bleem, M. Klein +149 more

Galaxy Clusters Selected via the Sunyaev-Zel'dovich Effect in 5 year data from the SPT-3G Main Survey

SZ-selected sample reaches median redshift 0.73 and mass 1.65e14 solar masses with 4.5 clusters per square degree

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We report a new galaxy cluster catalog, selected using the thermal Sunyaev-Zel'dovich (SZ) effect, from 5 years of observations of the SPT-3G Main field. Drawn from arcminute-resolution data with white noise levels of 3.2, 2.5, and 8.9 $\mu$K-arcmin at 95, 150, and 220 GHz, respectively, the sample consists of 8,892 cluster candidates detected above significance $\xi=4$, with an expected purity of $>82\%$ (4,480 at $\xi\ge5$ with purity $>99\%$). Using optical and infrared data we have confirmed 7,190 candidates as clusters. The sample spans a mass range $7.9 \times 10^{13}$ $M_\odot/h_{70}$ \ $< M_\textrm{500c} < $ $1.6 \times 10^{15}$ $M_\odot/h_{70}$ with a median mass of $1.65 \times 10^{14}$ $M_\odot/h_{70}$, and a redshift range of $0.037<z\lesssim 2$ with a median redshift of $z_{\textrm{med}}$ = 0.73; 1,780 clusters are at $z>1$ and 271 at $z>1.5$. Compared to previous SZ cluster samples from South Pole Telescope and Atacama Cosmology Telescope data, the SPT-3G sample is highly consistent in mass and redshift but is significantly deeper, with per-cluster detection signal-to-noise 2-4 times higher and a cluster density of 4.5 confirmed clusters/deg$^2$. We cross match with eRASS1 cluster and point source catalogs, finding 1,279 and 1,319 matches, respectively. The SPT and eROSITA cluster mass estimates are in relatively good agreement. We perform a series of validation checks using both internal data splits and comparisons to external samples. These tests show increasing correlated (dusty) emission with redshift, with a $\sim17\times$ larger 220 GHz temperature increment for clusters at $z\sim1.5$ than $z\sim0.25$, but only weak evidence for correlated synchrotron emission. Finally, a number of clusters are flagged as candidate strong gravitational lenses.

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astro-ph.GA 2026-07-02

Upper limit on CH2+ matches or undercuts model predictions

by M. Zannese, L. H. Coudert +15 more

Searching for the elusive CH2+ with the James Webb Space Telescope. Another carbocation to constrain astrochemical networks

Nondetection in Orion disk d203-506 places excited column density at or below thermochemical expectations when excitation matches CH+ and CH

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Carbocations are key species in interstellar chemistry, providing entry points for building larger hydrocarbons. CH+, and more recently, CH3+, have been detected. Other carbocations await detection to provide a comprehensive view of the astrochemical network that is at work in the interstellar medium. We search for CH2+ in objects in which CH3+ was detected and evaluate the most favorable conditions for detecting the elusive CH2+ reactive cation. We calculated the CH2+ rotational and rovibrational transitions expected to contribute in the mid- to far-infrared, focusing on the lower-energy rovibrational levels. We then calculated CH2+ infrared emission spectra at different excitation temperatures and compared them to JWST spectra of the externally irradiated disk d203-506 in Orion, where CH+ and CH3+ have already been detected. We used thermochemical models to predict the abundance and spatial morphology of CH2+ to better understand its nondetection. The comparison to JWST spectra allowed us to provide excitation-temperature-dependent upper limits to the excited column density. These are several times lower than those detected for CH+ and CH3+ in their excited states. Based on model calculations for photodissociation regions and assuming similar excitation temperatures, the upper limit derived from observations and CH2+ model spectrum is either slightly above or below the column density expected from models of photodissociation regions. We provide a list of tabulated transitions to allow the community to search for this carbocation in future observations as CH2+ is key in providing observational constraints on astrochemical models.

0

astro-ph.GA 2026-07-02

Faint galaxies supply most UV light at z=6

by Caio Moreira Goolsby, Christopher J. Conselice +7 more

Tilting at the Turnover: Modeling the Faint-End of the UV Luminosity Function Behind Abell s1063 with JWST

Lensed JWST data show sources below M_UV=-17 provide over half the luminosity density and 64% of ionizing photons.

abstract click to expand

We leverage the strong gravitational field of Abell S1063 to identify faint, highly magnified galaxies using ultra-deep James Webb Space Telescope (JWST)/NIRCam imaging from the GLIMPSE survey and ancillary Hubble Space Telescope (HST)/ACS imaging from the Hubble Frontier Fields program. We construct a photometric catalogue of lensed high-redshift candidates and use these sources to constrain the faint end of the rest-frame UV luminosity function (UVLF) over $z\simeq6$--11. Rather than treating the UVLF turnover ($M_{\rm t}$) as a hard cutoff, we model it as a gradual quadratic suppression and explicitly account for the potential continued contribution of galaxies beyond the turnover. In a shallow-turnover scenario, up to one-third of the UV luminosity density can arise from sources fainter than $M_{\rm t}$. While we find no direct evidence for a turnover down to $M_{\rm UV}=-13.5$ at $z=6$, our analysis can only confidently exclude weak, medium, and strong turnover models down to $M_{\rm t}=-15.9$, $-15.1$, and $-14.8$, respectively. Across these models, we infer lower limits of the UV luminosity, star formation density, and the ionization rate as: $\rho_{\rm UV}\geq22\times10^{25}\,{\rm erg\,s^{-1}\,Hz^{-1}\,Mpc^{-3}}$, ${\rm SFRD}\geq25\times10^{-3}\,M_\odot\,{\rm yr^{-1}\,Mpc^{-3}}$, and $\log_{10}(\dot{n}_{\rm ion}/{\rm s^{-1}\,Mpc^{-3}})\geq51.02$. We find that galaxies fainter than the conventional $M_{\rm UV}=-17$ limit contribute more than half of the UV luminosity density and at least $\sim64\%$ of the ionizing photons produced by star-forming galaxies at $z=6$. Because our turnover model permits a suppressed, but non-zero, galaxy population beyond $M_{\rm t}$, sources fainter than the turnover remain contributors to both $\rho_{\rm UV}$ and $\dot{n}_{\rm ion}$, emphasizing the need to consider the turnover and its shape during reionization.

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astro-ph.HE 2026-07-02

High-spin black hole masses trace low-spin merger remnants

by Yin-Jie Li, Yuan-Zhu Wang +2 more

Smoking-gun evidence for hierarchical black-hole mergers

Peak-by-peak match in 259 events shows high-spin black holes form via successive mergers rather than isolated processes.

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How stellar-mass black holes grow after their birth is a central open question in astrophysics. Gravitational-wave observations have revealed a subpopulation of coalescing black holes with both high masses and high spins, but whether these properties arise from hierarchical mergers in dense stellar environments or from accretion onto isolated black holes has remained unresolved. Here, using a flexible mixture population model applied to the 259 binary black hole mergers in GWTC-5, we show that the mass function of the high-spin subpopulation traces, peak by peak, the predicted remnant-mass distribution of the low-spin, stellar-collapse-origin subpopulation up to $\sim80\,M_\odot$. This morphological match, quantified by a Bhattacharyya coefficient as high as $\sim0.95$, is naturally expected if the high-spin black holes are themselves the products of earlier mergers, whereas any alternative scenario would require fine-tuning, thereby providing smoking-gun evidence for hierarchical mergers. In addition, the sharp upper-mass cutoff of the low-spin subpopulation at $m_{\rm max,1}=54.2^{+7.7}_{-7.2}\,M_\odot$ yields an astrophysical $S$-factor of $S_{300}=151^{+30}_{-26}$~keV~b (68\% credible interval) for the $^{12}{\rm C}(\alpha,\gamma)^{16}{\rm O}$ reaction, in agreement with the benchmark theoretical value. These results establish that the entire observed black-hole population can be accounted for by stellar collapse followed by dynamical hierarchical assembly, without invoking primordial black holes.

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astro-ph.GA 2026-07-02

Oxygen ratios and ages expose hidden Milky Way disk populations

by Thomas Bensby

Exploring the Milky Way stellar disk. Carbon, nitrogen, oxygen, sulphur, potassium, and copper abundances for 714 F and G dwarf stars in the solar neighbourhood

Measurements in 714 local stars show clearer old-young separations in [X/O] than in traditional [X/Fe] trends for several elements.

abstract click to expand

[ABRIDGED] We aim to determine abundances of carbon, nitrogen, sulphur, potassium, and copper for 714 nearby F and G dwarf and subgiant stars, and to re-derive oxygen abundances using updated corrections for departures from the assumption of local thermodynamic equilibrium. These elements extend the chemical inventory of our previous studies and provide new constraints on the relative enrichment histories of the Galactic thin and thick disks. The alpha-element behaviour of oxygen is confirmed, with old stars defining an enhanced sequence relative to young stars. Sulphur closely follows oxygen, while potassium shows broadly alpha-like behaviour in [K/Fe] but residual trends relative to oxygen. Carbon and nitrogen show only modest separation in [X/Fe], but much clearer population differences in [X/O]. Copper displays a strong metallicity dependence and clear separation between old and young populations when compared to oxygen. We also find that [O/Mg] is not constant, demonstrating that oxygen and magnesium provide complementary rather than interchangeable reference scales. Quantitative comparisons of all elements analysed in our studies show that carbon, oxygen, sulphur, and potassium rank among the most age-sensitive abundance ratios in the sample and provide strong discrimination between old and young disk populations. The new abundance measurements substantially expand the diagnostic power of this local stellar sample. The results show that abundance ratios relative to oxygen, together with precise stellar ages, reveal population differences that are partly hidden in traditional [X/Fe] trends. The expanded abundance inventory provides a homogeneous reference dataset for studies of Galactic chemical evolution, Galactic archaeology, and large spectroscopic surveys.

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astro-ph.GA 2026-07-02

X-shaped bulge already complete in galaxy 7.6 billion years ago

by Takafumi Tsukui, Zeyu Gao +5 more

Bar-driven secular evolution largely complete in a disk galaxy 7.6 billion years ago

JWST finds bar-driven secular evolution largely finished when the universe was less than half its current age

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Disk galaxies like the Milky Way are thought to evolve through internal dynamical processes: the stellar disk forms a bar, the bar drives gas inflow that builds a nuclear stellar disk, and the bar vertically thickens into an X-shaped bulge. Although this evolution is thought to be slow, completing only at late cosmic times, its timing remains poorly constrained. We report James Webb Space Telescope imaging of a galaxy at redshift 0.92 (7.6 billion years ago) that already hosts an X-shaped bulge, a nuclear stellar disk, and an extended stellar disk, with geometry and inferred bar size indistinguishable from those of present-day barred galaxies. The X-shaped bulge marks the completion of the major phase of bar-driven evolution when the Universe was less than half its current age.

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astro-ph.GA 2026-07-02

Milky Way filaments show no strong B-field alignment

by Naval K. Bhadari, Ke Wang +2 more

The Milky Way Atlas for Linear Filaments III: Giant filaments and magnetic fields as evidence of a bubbly Galactic disk

Observations favor supernova shells over magnetic forces, implying a bubbly disk when viewed face-on.

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Linear filamentary structures are fundamental constituents of the interstellar medium and play a central role in star formation. Their relative orientation with respect to the ambient magnetic field (B-field) provides key constraints on filament formation mechanisms. We investigate the relative orientation between Milky Way linear filaments (MWLFs) and the plane-of-sky B-field using polarization observations from the Atacama Cosmology Telescope (ACT) DR6, complemented by Planck data. Filament orientations are compared with the local B-field and the Galactic plane, while projection effects and statistical significance are quantified using Monte Carlo simulations of vector pairs in three-dimensions. We find no strong preferential alignment between MWLFs and the ambient B-field. Although the B-field is preferentially aligned with the Galactic plane with relative angles $\theta_{\rm BG} \sim0-25\deg$, filament orientations exhibit a bimodal distribution, being either parallel or perpendicular to the plane ($\theta_{\rm FG} \sim0-15\deg$ and $\sim75-90\deg$). Filaments located far from the Galactic midplane ($|z|>90$ pc) preferentially show perpendicular alignment with both the plane and the B-field, whereas those near the midplane exhibit a bimodal orientation. These results indicate that large-scale B-fields do not dominate the formation of MWLFs and instead favor a super-Alfv\'enic regime in which magnetic forces are dynamically subdominant, as expected for filaments associated with supernova-driven shells. Overall, our findings suggest that a face-on view of the Milky Way would resemble nearby disk galaxies such as M74, as observed in JWST images, with its disk structured by a network of supernova-driven bubbles (i.e., a bubbly disk).

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astro-ph.GA 2026-07-02

Edge-on galaxies show Type II breaks in 90 percent of disks

by Sergey S. Savchenko, Ilia V. Chugunov +6 more

Projection-Enhanced Disk Breaks: Evidence from Deep Photometric Decomposition

Projection effects raise the apparent contrast of downbending breaks when disks are viewed sideways, producing a higher fraction than seen i

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Radial brightness profiles of disk galaxies often exhibit so-called breaks -- locations where their exponential-scale length abruptly changes. Some galaxies have downbending (Type II) breaks, where their brightness decays faster in outer regions, while other have upbending (Type III) breaks, resulting in more extended outer disks or envelopes. Disk radial profiles without any breaks (Type I) appear to constitute a minority. The exact fractions of different break types depend on many galactic parameters -- such as Hubble type, stellar mass, spatial environment, and bar presence -- and vary significantly across different studies. Another source of discrepancy is the orientation of galaxies: projection effects may play an important role in break detectability. In this work, we utilize DESI Legacy DR10 imaging to perform photometric decomposition of a sample of 375 edge-on galaxies and investigate their radial breaks. We find that the vast majority (~90%) of disks in our sample have Type II breaks, which is a considerably higher fraction than in many previous works (~50%). We carefully tested our results to check if observed breaks can be a result of flaring or two-disk composition. We showed that a high fraction of Type II breaks can be attributed to projection effects, which enhance the observed surface brightness of breaks in edge-on galaxies.

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astro-ph.GA 2026-07-02

Spectroscopy detects pre-2019 accretion in Ansky QPE host

by P. Sánchez-Sáez, M. Masterson +26 more

Spatially resolved optical and mid-infrared spectroscopy of SDSS1335+0728: implications for the origin of the Ansky event

Minimum ionising output sustained 1500 years favors faint AGN or TDE remnant disc over faded AGN for the 10^6 solar-mass black hole

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The galaxy SDSS1335+0728 brightened abruptly in December 2019 (the Ansky event) and has since been confirmed as the host of extreme X-ray quasi-periodic eruptions (QPEs) of debated origin. We constrain the origin of its transient activity by characterising the galaxy properties and nuclear accretion history with spatially resolved VLT/MUSE and JWST MIRI/MRS spectroscopy. We extract stellar and gas kinematics and emission-line fluxes, construct emission-line ionisation diagnostic maps, reconstruct the nuclear ionisation history via a Balmer-line light-echo analysis, and measure the mid-infrared silicate feature strength. The stellar kinematics reveal two counter-rotating stellar regions and kinematically cold gas ($\sigma_{\rm gas} \lesssim 60$ km s$^{-1}$), consistent with a past minor merger. Stellar populations show an old host with ongoing star formation confined to a ring at intermediate radii. Ionisation diagnostics reveal a three-zone structure: a central region powered by SMBH accretion, where high-ionisation coronal lines ([NeVI]$\lambda7.65\mu$m, [NeV]$\lambda14.32\mu$m, [OIV]$\lambda25.89\mu$m) are confined, a star-forming ring, and a LINER-like outer region. A Balmer-line light-echo analysis yields a minimum ionising luminosity $\log L_{\rm ion,min} \approx 40.5$ erg s$^{-1}$ sustained over at least $\sim 1\,500$ yr. Broad silicate emission at 9.7 and 18$\mu$m indicates optically thin dust, inconsistent with a classical active galactic nucleus (AGN) dusty torus. The data are consistent with two scenarios for the pre-2019 accretion: a persisting or gradually fading low-luminosity AGN, or a long-lived tidal disruption event (TDE) remnant disc. In both, Ansky corresponds to a slow, faint transient in a $\sim\!10^6\,M_{\odot}$ SMBH with already ongoing accretion, challenging the "faded AGN" interpretation proposed for some QPE hosts.

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astro-ph.GA 2026-07-02

Kolmogorov cascade spans 0.05 to 20 parsecs in Polaris Flare

by Xunchuan Liu, Pak-Shing Li +1 more

Kolmogorov turbulence across multi-fractal gas in Polaris Flare

Mapping shows the apparent break at 0.5 pc comes from projection and density changes, not a shift in turbulent regime

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We reveal a pristine, scale-invariant 3D Kolmogorov velocity cascade ($\alpha_V^{\mathrm{3D}} \sim 2/3$) spanning $0.05$--$20$~pc in the Polaris Flare using \texttt{PPCOS} $^{12}\text{CO}$ data. A transition scale at $\sim 0.5$~pc marks a bifurcation in the structure functions' exponents, below which the degree of intermittency is also saturated. By deriving an analytical mapping relation ($\alpha_V^{\mathrm{3D}}=\alpha_V-\frac{1}{3}\alpha_I$), we obtain the scale-invariant value of $\alpha_V^{\mathrm{3D}}$, proving that the apparent transition stems from geometric projection and a changing density fractal dimension rather than a turbulent mode shift. Kolmogorov turbulence is smoothly inherited from the large-scale cold neutral medium, remaining uninterrupted by compression or gravity below 0.1 pc.

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astro-ph.HE 2026-07-02

SKAO surveys to discover thousands of pulsars

by Bhal Chandra Joshi, Aris Karastergiou +1 more

Pulsar Science with the SKAO

High-sensitivity telescopes will support deep observations feeding tests of gravity, nano-Hz waves and nuclear matter.

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The large instantaneous sensitivity, wide frequency coverage and flexible observation modes, with large number of beams in the sky, are the main features of the SKA observatory's two telescopes, the SKA-Low and the SKA-Mid. Owing to these capabilities, the SKAO telescopes are going to be a game-changer for radio astronomy in general and pulsar astronomy in particular. Eleven chapters in this book describe their impact on different areas of pulsar science. In this overview article each chapter is briefly summarised and the inter-relationship between different pulsar science use cases are explored: new deep surveys, covering the Galactic field, globular clusters and the Galactic centre, will discover thousands of new pulsars; these will form the backbone for studies of neutron star physics and of their environments. The enhanced understanding provided by these studies will feed into the main contributions to fundamental physics from pulsar astronomy: testing relativistic gravity, studying gravitational waves in the nano-Hz regime and studying the equation of state of nuclear matter. Synergies with other science cases are also highlighted throughout this overview.

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astro-ph.CO 2026-07-02

Oldest Milky Way stars reach 13.73 Gyr

by Indranil Banik, Thenujaya Kudakolawa Kaluarachchige +2 more

The age of the Universe from a large sample of the oldest Galactic stars

Large spectroscopic sample yields age consistent with 13.6 Gyr Lambda-CDM but inconsistent with 12.9 Gyr pre-recombination Hubble-tension mo

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We estimate the age of the Universe using the Xiang & Rix sample of 247,103 Milky Way stars with high-resolution spectroscopy from LAMOST DR7 and $Gaia$ eDR3 parallaxes. Stellar ages were estimated using YY isochrones up to 20 Gyr. To remove stars with unusually high and precise ages, we require old stars to be metal-poor and $\alpha$-enriched. We also require consistency between YY ages and those obtained with FLAME based only on $Gaia$ data. Our final sample of 155,600 stars within 5 kpc provides consistent cosmic age estimates using several techniques of increasing rigour. Our main results use an MCMC reconstruction of the latent age distribution, though our iterative reconstruction is very similar. Applying an innovative approach to our MCMC reconstruction and its uncertainties, we find that the oldest star has an age of $A_\star = 13.73^{+0.18}_{-0.15}$ Gyr. Varying the quality cuts can at most reduce this to $A_\star = 13.31^{+0.21}_{-0.18}$ Gyr or raise it to $14.02^{+0.18}_{-0.15}$ Gyr using a much lower or higher age-dependent metallicity ceiling, respectively. Our inferred $A_\star$ is consistent with the 13.6 Gyr expected in CMB-calibrated $\Lambda$CDM, assuming the first long-lived stars formed when the Universe was 0.2 Gyr old. This agreement casts doubt on solutions to the Hubble tension solely through new physics prior to recombination, which generally imply a cosmic age of $12.9 \pm 0.2$ Gyr to match low redshift probes. It is difficult for stellar modelling uncertainties to reconcile such a low age with our result given the low metallicities of the oldest stars in our sample and independent asteroseismic constraints.

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astro-ph.SR 2026-07-02

Brown dwarf spectra favor weak mixing Elf Owl models

by Zafar Rustamkulov, J. Kirkpatrick +22 more

SPHEREx 0.75 to 5 μm Spectra for a Sequence of Nearby Brown Dwarfs

SPHEREx data on 37 nearby objects show clear preference for low k_zz over strong mixing despite offsets near CO features.

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The SPHEREx all-sky survey has now measured the R$\sim$40-100 infrared spectra of thousands of nearby brown dwarfs in the chemically rich 0.75-5 $\mu$m range. The survey's wide spectral coverage and high S/N permits flux measurements that capture several broadband molecular absorption features, and upwards of 80$\%$ of the total bolometric luminosity of most brown dwarfs. Atmospheric models are known to yield systematic disagreements in the inferred temperatures and radii of brown dwarfs, necessitating benchmarking against observations. In this work, we present SPHEREx spectra across a broad sequence of 37 nearby field brown dwarfs, ranging from L0 to Y4 ($\sim$2500-250 K) and compare them to theoretical expectations. We additionally compile spectra for separate low-gravity and low-metallicity objects, and show how they trend with constant spectral type. We fit the measured spectra to the well-known forward model grids Sonora Diamondback, Elf Owl, BT-Settl, ATMO2020 and ATMO2020++ and compare their goodness-of-fit as a function of wavelength, spectral type, and treatment of clouds and chemistry. We find that the models continue to struggle to simultaneously fit the J/H/K peaks and the 4 $\mu$m opacity window, especially in L/T transition objects. The largest deviations appear around the chemistry-sensitive CO$_2$ and CO features. Despite these offsets, the models broadly capture their trends across the L/T transition, with the observed sample of field dwarfs strongly preferring the weak vertical mixing ($k_\mathrm{zz}$ = 10$^4$ cm$^2$s$^{-1}$) Elf Owl models over strong mixing. The spectra shown here along with future SPHEREx data will help guide improvements to models.

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astro-ph.GA 2026-07-02

NGC 1381 hosts ancient slow bar with accreted components

by Yunpeng Jin, Ling Zhu +5 more

Dissecting the 3D chemo-dynamical structures of NGC 1381: a galaxy hosting an ancient slow bar with an accreted bulge and thick disc

Six-component decomposition shows bar, nuclear and thin discs formed in place while bulge and thick disc were accreted

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We applied the barred population-orbit superposition method developed in \citet{Jin2025a,Jin2025b} to construct 3D chemo-dynamical models for the barred S0 galaxy NGC~1381 in the Fornax cluster. Based on the stellar orbits in the models, we decomposed NGC~1381 into six components: (1) a dynamically warm nuclear disc with $f_{\rm nucl}\sim5\%$; (2) a rigidly rotating, BP/X-shaped bar with $f_{\rm bar}\sim30\%$; (3) a dynamically hot, spheroidal bulge with $f_{\rm bulge}\sim17\%$; (4) a dynamically cold thin disc with $f_{\rm thin}\sim28\%$; (5) a vertically extended thick disc with $f_{\rm thick}\sim16\%$; and (6) a dynamically hot, spatially diffuse stellar halo with $f_{\rm halo}\sim5\%$. The nuclear disc, bar, and thin disc are metal-rich ($[Z/\rm H]\gtrsim0$), $\alpha$-poor ($\rm[Mg/Fe]\lesssim0.2$), and old ($\sim13\rm\,Gyr$), corresponding to in situ formation in the early Universe. The bulge, thick disc, and stellar halo are metal-poor ($[Z/\rm H]\lesssim0$), $\alpha$-rich ($\rm[Mg/Fe]\gtrsim0.2$), and younger than or comparable in age to the in situ components, suggesting their relations with ex situ formation contributed by minor mergers. The flat metallicity and [Mg/Fe] gradients in the thick disc and stellar halo indicate they are dominated by a similar population of ex situ stars. In contrast, the bulge exhibits a negative metallicity gradient ($\nabla[Z/\rm H]_{bulge}<0$) pointing to a more complex formation history: the bulge could be either predominantly ex situ or contain a non-negligible mixture of in situ and ex situ stars. Our modelling also reveals the presence of a slow bar ($\mathcal{R}=2.40_{-0.27}^{+0.54}$), with a bar pattern speed of $\rm\Omega_p=34_{-7}^{+4}\,km\,s^{-1}\,kpc^{-1}$, a bar length of $R_{\rm bar}=2.24_{-0.22}^{+0.43}\rm\,kpc$, and a corotation radius of $R_{\rm CR}=5.38_{-0.28}^{+1.59}\rm\,kpc$, which is consistent with its ancient formation time.

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astro-ph.GA 2026-07-02

Superthin galaxies stay thin from optical to near-infrared

by Jianhong Hu, Cheng Li +1 more

Optically Selected Superthin Galaxies Remain Thin in the Near-infrared

Axis ratios remain constant while sizes shrink, showing no thick old-star disk and favoring low-density halo environments.

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We investigate whether galaxies identified as superthin in optical images remain superthin in the near-infrared (NIR), and how their extreme disk morphology is related to environment. From a nearby volume-limited sample, we select 210 superthin galaxies using two-dimensional bulge/disk decomposition of SDSS $r$-band images, requiring the disk component to have a major-to-minor axis ratio $a/b>9$. We measure disk shapes from SDSS $griz$ to UKIDSS $JHK$ bands. Both the major- and minor-axis scales decrease from the optical to the NIR, reaching $\sim0.6$ of their $r$-band values in the $K$ band, but the disk axis ratio remains nearly unchanged. Thus, optically selected superthin galaxies remain superthin in the NIR, implying that the old stellar populations traced by NIR light do not form a prominent thick disk. Reanalysis of our sample and a previous superthin sample shows that earlier reported NIR thickening is mainly due to a magnitude- and band-dependent bias in one-dimensional fitting. We further compare their environments with matched control samples using projected cross-correlations, reconstructed local overdensities, and large-scale-structure classifications. Superthin galaxies show lower clustering on $\sim0.1$--$1\,h^{-1}\,\mathrm{Mpc}$ scales and lower overdensities at $1\,h^{-1}\,\mathrm{Mpc}$, but no clear residual dependence on large-scale-structure type. These results suggest that superthin galaxies are preferentially central galaxies in relatively low-mass dark matter halos, consistent with a picture in which high host-halo spin helps build and preserve extended, vertically thin stellar disks.

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astro-ph.GA 2026-07-02

Merged SITELLE and MUSE data cuts metallicity gradient scatter to 0.04 dex

by Eric Habjan, Kathryn Kreckel +15 more

Exploring the synergies of [O\,II]λ 3727 with MUSE spectroscopy in PHANGS H II regions

A catalog of 604 nebulae recovers calibration offsets yet shows consistent radial trends and identifies [S III]/[S II] as a cleaner ionizati

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Spatially resolved maps of gas-phase metallicity provide key constraints on the chemical enrichment and mixing processes that drive galaxy evolution, but measurements based only on strong lines remain highly uncertain and dependent on emission-line coverage. In this work, we present a joint analysis of SITELLE observations, covering the $[O II]\lambda\lambda3726,3729$ doublet, with PHANGS-MUSE spectroscopy covering 4800-9300 Angstroms, including $H\beta$, $[O III]\lambda4959,5007$, $[N II]\lambda6584$, $H\alpha$, $[S II]\lambda\lambda6716,6731$, and $[S III]\lambda9069$, within five nearby spiral galaxies. By combining these data, we construct a homogeneous catalog of emission-line fluxes for 604 ionized nebulae, 556 of which are classified as H II regions. This enables a comparison of eight widely used strong-line metallicity calibrations, five new strong-line calibrations, and an investigation of ionization-parameter diagnostics. We recover known systematic offsets among calibrations, but also find that many exhibit very low scatter, less than 0.03-0.04 dex, in radial metallicity gradients. We find that $[S III]/[S II]$ exhibits minimal secondary dependence on metallicity or extinction, suggesting that it may be a more robust tracer of ionization parameter than $[O III]/[O II]$. No significant outliers are identified in O/H or N/O within the sampled regions, indicating internally consistent abundance trends across the inner disks probed by our data. We provide a publicly available catalog of all measured emission-line fluxes, designed to support future investigations, including temperature modeling and strong-line abundance calibrations.

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astro-ph.HE 2026-07-02

Companion interaction cannot explain asymmetric SNR expansion rates

by Jingxiao Luo, Gilles Ferrand +3 more

Three-Dimensional Simulations of Type Ia Supernova Remnants I: Effects of a Main-Sequence Companion Star

3D models of Type Ia ejecta colliding with a main-sequence star reproduce some remnant shapes but fall short on the large velocity differenc

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Type Ia supernovae (SNe Ia) serve as one of cosmic standard candles, but their exact progenitor channel is still an open question. SNe Ia commonly come from binary star evolution. Therefore, one of the major differences among the proposed progenitor channels is whether there is a more-or-less intact companion star remaining at the time of explosion, which causes the SN ejecta to be more asymmetrical. As the SN ejecta evolved into supernovae remnants (SNR), the imprint formed by the companion interaction may affect the morphology of the SNR. In addition, the progenitor systems may have experienced different mass transfer histories and therefore led to formation of different circumstellar material (CSM) environments, which may also affect the early evolution of SNR. In this study, we use GADGET and RAMSES codes to simulate these physical effects and follow the evolution into early-phases of SNRs. In our simulations, we consider different ejecta models and track the element distribution. We compare our simulation with actual observations and conclude that despite some SNRs having morphology resemblance to our simulation results, their highly asymmetric expansion rates are hard to explain by interaction between SN ejecta and a companion star alone.

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astro-ph.HE 2026-07-02

Mass ratio sets period of microlensing fluctuations in binary black holes

by Changshuo Yan, Youjun Lu

Multiwavelength periodic microlensing signatures of macrolensed supermassive binary black holes

Equal-mass pairs vary at half the orbital period while low-mass-ratio pairs follow the full period, with larger amplitudes at shorter wavele

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The microlensing of lensed quasars presents a promising avenue for understanding the structure of accretion disks around supermassive binary black holes (SMBBHs). We investigated the microlensing signatures in multiband (optical, UV, and X-ray) light curves of active SMBBH systems, focusing on how these signatures depend on the mass ratio, separation, and accretion rate. We analyzed the periodic fluctuations in microlensing light curves induced by the orbital motion of SMBBHs. We examined the relation between the mass ratio and the period of variations in light curves across optical, UV, and X-ray bands. We find that the periodic fluctuations in the light curves depend on the mass ratio of the black holes: for nearly equal masses, variations occur at half the orbital period, whereas for low mass ratios, the period corresponds to the orbital period influenced by the secondary mini-disk. Furthermore, all optical, UV, and X-ray light curves exhibit the same period and phase, but the amplitude of variation is greater in the UV and X-ray bands than in the optical bands. These light curves provide insights into the motion and radiation regions of the disks through wavelength-dependent periodic variations, although they yield limited constraints on the system's black hole mass or Eddington ratio, which can instead be derived from the spectral energy distribution (SED). Integrating microlensing data with SED observations is crucial for accurately constraining the parameters of SMBBH systems.

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astro-ph.GA 2026-07-02

SKA to map magnetic fields from stars to cosmic web

by Tessa Vernstrom, Jennifer L. West +1 more

Cosmic Magnetism Science with the SKA

Planned observations will test how magnetism shapes structure formation at scales from planets to the Universe.

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Magnetic fields are a fundamental component of astrophysical systems, yet many key questions about their origin, amplification, and role in structure formation and evolution remain unresolved. The SKA will mark a transformational step forward in addressing these questions, enabling studies of cosmic magnetism across a large range of spatial scales and environments. This overview summarizes the main science cases in the Cosmic Magnetism Science Working Group, which cover a huge breadth of scales from the smallest scales governing planet and star formation, all the way up to the large-scale structure of the Universe. The chapter summarizes the main observational techniques for studying magnetic fields, including direct polarization imaging, Faraday rotation, rotation-measure grids, and Zeeman splitting. We also address fundamental considerations of these studies including SKA-Low vs SKA-Mid and wide-area vs deep observing strategies.

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astro-ph.GA 2026-07-02

VLBI detects buried AGN in merging galaxy UGC 2369S

by Wancheng Xu, Sándor Frey +2 more

Direct VLBI evidence for a buried AGN in the triple-merger LIRG UGC 2369S

Compact source with high brightness temperature and flat spectrum confirms obscured nucleus in triple-merger LIRG

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UGC 2369S is a luminous infrared galaxy (LIRG) undergoing a late-stage merger in a triple system, where the heavily obscured northern core is suspected to host an active galactic nucleus (AGN). However, severe dust and gas obscuration makes definitive confirmation challenging. We aim to provide direct observational evidence for the buried AGN through high-resolution radio imaging, while investigating the AGN accretion and feedback properties within this merger-driven gas-rich environment. We analyzed archival European VLBI Network (1.6 GHz) and Very Long Baseline Array (1.7 and 5 GHz) data of UGC 2369S. Through high-resolution imaging and visibility-domain Gaussian modeling, we characterized the morphology and intensity of its milliarcsecond-scale radio emission. A compact radio component is detected at the northern core, exhibiting high brightness temperature ($T_{\rm b}>10^7$ K) and flat radio spectrum ($\alpha \approx -0.45$), which confirms the presence of an obscured AGN. The sub-Eddington accretion rate ($\lambda_{\rm Edd} \approx 2.7 \times 10^{-4}$) indicates that it falls within the radiatively inefficient accretion flow (RIAF) state. We provide direct imaging evidence for an AGN in the northern core of UGC 2369S, revealing a deeply buried, jet-emitting low-luminosity AGN (LLAGN) enshrouded by a Compton-thick gas cocoon. This demonstrates that VLBI is a uniquely effective tool for disentangling nuclear accretion and feedback processes within the heavily obscured environments of multiple-merger systems.

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astro-ph.GA 2026-07-02

Spectral index in AGN changes with telescope resolution

by Yuki Kudoh, Satoko Sawada-Satoh

Probing the Parsec-Scale Dynamical Structure of Ionized Gas in Radio-Quiet AGN with SKA

Beam size alters the mix of jets, outflows and star formation sampled, so SKA can map each at its native scale

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We systematically organize the radio-emitting components in radio-quiet active galactic nuclei (RQ AGN), including jets, accretion disk coronae, dust, ionized gas outflows, and circumnuclear star formation. We present a diagnostic framework for distinguishing these components using spectral turnovers and spectral indices produced by synchrotron self-absorption (SSA) and free-free absorption (FFA), together with brightness temperature and peak frequency. The central premise is that the observed spectral index and its spatial distribution are not unique source properties unless the observing beam is specified: changing the angular resolution changes the physical scale being sampled and therefore changes the mixture of radio-emitting components. By exploiting this scale dependence with SKA1-MID and SKA-VLBI, spatially resolved spectral-index mapping will reveal which physical processes dominate from circumnuclear star formation on $\sim$100 pc scales to jets, coronal emission, and compact ionized gas on parsec and sub-parsec scales. Through multi-frequency continuum imaging and spectral-index mapping, SKA observations will provide a multi-scale physical view of radio-quiet AGN that links radio emission mechanisms to accretion, obscuration, and feedback.

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astro-ph.CO 2026-07-02

Low-frequency data separate synchrotron from free-free emission

by Daniel Robins, Dominic Anstey +3 more

Synchrotron and free-free mapping with simulated REACH observations between 50-170 MHz

Joint fitting recovers synchrotron maps across the sky at 50-170 MHz while free-free recovery stays limited.

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Global 21cm experiments aim to detect the hydrogen 21cm signal by separating it from foreground emission that can be orders of magnitude brighter than the signal. REACH (the Radio Experiment for the Analysis of Cosmic Hydrogen) forward-models the sky by jointly fitting signal and foreground spectral parameters to an existing sky map. The fitted parameters yield spectrally constrained, absolutely calibrated maps of the radio sky across the full 50-170 MHz observing band, among the lowest continuous frequencies yet mapped. We assess REACH's ability to fit the 21cm signal and recover accurate foreground maps, using physically motivated foreground models of increasing complexity (starting from a pure synchrotron power law model, then introducing variable amplitudes, curvature, and a free-free component). We evaluate these models against simulated REACH observations of correspondingly complex foregrounds, based on the Global Sky Model and the Python Sky Model. To recover the 21cm signal, more complex datasets require correspondingly complex models, but this introduces degeneracies which limit accurate recovery of foreground parameters. Fitting a foreground with independent synchrotron and free-free emission enables component-separated sky mapping, which has applications beyond radio cosmology; synchrotron is well-recovered across the sky, but free-free recovery is limited. REACH is therefore capable of probing Galactic physics at uniquely low frequencies, alongside its primary goal of detecting the 21cm signal.

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astro-ph.GA 2026-07-02

Neutron-capture elements show flat Milky Way gradients

by Natalie R. Myers, Peter M. Frinchaboy +11 more

OCCAM X. Neutron Capture Abundances with Keck/HIRES & Magellan/MIKE

Second-peak s-process and r-process abundances lack the steep radial slopes of alpha and iron-peak elements in 18 open clusters.

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The chemistry of stars provides powerful insight into the history of the Milky Way. With multiple large-sky spectroscopic surveys that are currently available, using chemistry as a means to study the evolution and history of the Milky Way has flourished. Open clusters have long been used as landmarks to calibrate different age dating methods (e.g., gyrochronology and asteroseismology). In this work, we utilize the SDSS-IV/APOGEE-based Open Cluster Chemical Abundances and Mapping (OCCAM) survey as our foundation for new optical observations; enabling us to characterize neutron-capture abundances for known cluster members. For 56 stars in 18 open clusters, we collected high-resolution (R > 50,000), high-S/N (>75 at 5500A), spectra from Keck I and Magellan Baade telescopes. With these data, we derive abundances for 23 elements using BACCHUS, including 7 neutron capture abundances not measurable by APOGEE. Finally, we characterize the radial distribution of these neutron-capture elements in the Milky Way. We find that the second-peak s-process and r-process abundances exhibit relatively flat gradients in the Milky Way. Although not as distinct, the first-peak s-process abundances also have slopes which are shallower than the alpha and iron-peak elements. The differences in the neutron-capture gradients from the lighter elements not just indicates the sources producing these elements are fundamentally different, but that the timescales on which they are produced also differ (especially for the r-process). Moreover, a metallicity dependence of the AGB stars responsible for producing the heaviest s-process abundances may be necessary to consider in Galactic evolution models.

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astro-ph.SR 2026-07-01

Gaia DR4 pipeline to give masses and ages for 500 million stars

by Orlagh L. Creevey, Laia Casamiquela +24 more

Stellar masses and ages in Gaia Data Release 4 from the Final Luminosity Age Mass Estimator algorithm

FLAME combines analytical luminosity-radius steps with Bayesian or minimization fitting on Gaia data to produce the estimates.

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The masses and ages of stars are key quantities for understanding exoplanetary, stellar, and galactic evolution. In the context of Gaia, these parameters provide insights into the stellar populations, helping to trace the formation and history of the Galaxy. As part of the Gaia Data Processing and Analysis Consortium (DPAC), the Final Luminosity Age Mass Estimator (FLAME) pipeline processes Gaia data to derive stellar parameters comprising luminosities, radii, masses and ages. This paper discusses the methods and data used in FLAME for Gaia Data releases and the expected performances of FLAME for the 4th Gaia Data Release. FLAME comprises two main components: the first one, which is analytical, is used to estimate luminosity, radius, and radial velocity correction due to gravitational redshift by exploiting the atmospheric, astrometric, and photometric parameters produced within Gaia. The second is a model inference based on two main approaches: a classical minimization approach, and a Bayesian framework. It aims to derive mass, age, and evolutionary stage. The two step implementation offers flexibility in handling photometric properties that are prone to systematic errors. Tests with simulated data, the Sun, and well characterised samples of stars show that the methods in FLAME perform as expected, producing results in statistical agreement with the literature. We provide new stellar fundamental parameters for some high velocity stars, stars with very low mass companions, and a selection of stars in the Plato Field of View. In Gaia Data Release 4 approximately 500 million sources will have results from the pipeline. [abridged]

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astro-ph.GA 2026-07-01

SHARP delivers H0 from infrared lags in dozens of AGN

by M. Signorini, V. N. Bennert +4 more

Precision near-IR spectroscopy for understanding AGN physics and shed light on the H0 tension -- SHARP Science Book

Multi-object near-IR spectroscopy on the ELT enables time-delay measurements for many more active galactic nuclei, supporting geometric dist

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The persistent tension between early- and late-Universe measurements of the Hubble constant (H0) remains on of the most significant challenges in modern cosmology. The Spectroastrometry and Reverberation Mapping (SARM) method offers a promising, calibration-independent approach to address this issue by combining time-delay measurements of the Broad-Line Region (BLR) with interferometric angular size determinations. Current implementations of SARM, however, are limited by the difficulty of performing near-infrared reverberation mapping (RM) on the same emission lines observed by GRAVITY, restricting applications to only a few bright AGN. We propose using the capabilities of SHARP, the next-generation near-infrared spectrograph for the Extremely Large Telescope (ELT), to overcome these limitations. SHARP's sensitivity and multi-object spectroscopy will enable (1) efficient long-term monitoring of existing GRAVITY targets with minimal time investment, and (2) systematic RM campaigns for the fainter AGN that will be observed by GRAVITY+. These advances will give us precise infrared lags for tens of AGN, enabling geometric distance measurements and a robust, calibration-free determination of H0. Beyond cosmology, SHARP will allow detailed studies of BLR structure and kinematics in the infrared, advancing our understanding of AGN physics and with repercussion on the measurements of Supermassive Black Holes (SMBH) masses.

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astro-ph.GA 2026-07-01

JWST high-z clumps evolve into globular clusters in simulations

by A. Della Croce, E. Vesperini +5 more

The evolution of high-z proto-star clusters into local globular clusters

Multiple-population systems survive strong early tides and match Galactic GC properties after 12 Gyr.

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The James Webb Space Telescope (JWST) detected numerous massive and relatively compact stellar clumps around proto-galaxies at high redshift (z>0.5). Their properties suggest that these systems may represent proto-globular clusters (GCs), but their possible connection to local old GCs is poorly understood. In this Letter, we explore the dynamical evolution of proto-star clusters, building the missing evolutionary link between high-z systems observed by JWST and local GCs. Our simulations include the effects of stellar interactions, stellar evolution, and the strong time-dependent cosmological tidal field in which these proto-star clusters evolve. We also explore the role of multiple stellar populations and stellar-mass black holes (BHs), two fundamental ingredients in stellar cluster dynamics. We show that systems hosting multiple populations (as routinely observed in local GCs) are more likely to endure the early strong tidal field than single-population clusters. In addition, after 12 Gyr, such systems have properties consistent with those of Galactic GCs. Our work confirms that the high-z clumps observed by JWST can be the progenitors of the local GCs. Finally, we show that a population of stellar-mass BHs within a proto-star cluster favors its disruption, but that surviving systems can retain a sizable population of BHs.

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astro-ph.EP 2026-07-01

Microbes may survive galactic travel inside icy interstellar objects

by Shokhruz Kakharov, Abraham Loeb

Prospects for Panspermia via Interstellar Objects like 3I/ATLAS

JWST data on 3I/ATLAS shows ice allows low-rate survival, though directed planting fails due to destructive impact energies.

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We study the feasibility of natural and directed panspermia via interstellar objects (ISOs) like 3I/ATLAS. The paper is organized around two questions. First, could natural panspermia occur if microbes or biomolecules survived inside shielded ice and were later exposed during perihelion and outbound activity? Second, could directed panspermia occur if a technological civilization planted life-bearing material inside or onto an icy ISO so that it later transported life through the Milky Way? We combine data on 3I/ATLAS with order-of-magnitude thermal, biological, and mission constraints. SPHEREx provides the volatile and organic context through CO$_2$, H$_2$O, CO, dust, and a broad C--H feature, while JWST/MIRI provides the first direct CH$_4$ detection in an interstellar object and confirms an unusual volatile inventory, including enhanced CO$_2$:H$_2$O and CH$_4$:H$_2$O ratios. We distinguish dormant interstellar cruise from active perihelion. Natural panspermia is plausible as microbes can survive or repair damage in ice films, veins, or frozen matrices at very low metabolic rates. Methane production is more nuanced. Frozen survival metabolism would require $\sim10^{14}$--$10^{15}$ kg of biomass to match the JWST CH$_4$ rates, but active methanogenic archaea in warm, liquid, substrate-rich settings can produce methane many orders of magnitude faster, reducing the required biomass in optimistic laboratory-rate comparisons. Directed panspermia faces a different challenge: a direct 60 km s$^{-1}$ impact releases $1.8\times10^9$ J kg$^{-1}$, hundreds of times the specific energy of TNT, and would destroy a biological capsule. 3I/ATLAS-like objects are therefore best treated as test cases for panspermia diagnostics rather than as evidence for life. Natural panspermia requires preservation plus a credible liquid-water or near-surface activation pathway.

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astro-ph.GA 2026-07-01

Multiple methods narrow the search for the universe's first stars

by Alessandra Venditti, Daniel Schaerer +27 more

How can we finally see the first light? Status and perspective in the search for Population III stars

JWST spectroscopy, lensing, and archaeology together shrink the allowed properties of Population III stars and ready the field for detection

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Finding the first (Population III or Pop III) stars is one of the fundamental quests of astronomy, aiming to deliver the missing link in how stars form at early cosmic times. Yet their initial mass function, formation sites and feedback remain highly uncertain, as well as the timing and topology of the transition to metal-enriched star formation. The observability of their peculiar spectral features is also debated, due to their short lifetime and faintness. This review summarizes current theoretical expectations for Pop III star formation, and the main observational strategies that have been adopted to constrain their properties across cosmic time, including near-field cosmology studies, direct searches for extremely metal-poor star-forming complexes and/or hard-ionizing spectral signatures at high and intermediate redshifts, and prospects for identifying Pop III activity up to Cosmic Dawn. The combination of JWST spectroscopy, time-domain searches, lensing surveys, stellar archaeology, absorption-line studies, as well as improved simulations, is yielding a growing number of observational candidates and narrowing the allowed parameter space for the first stars, setting the stage for a ``golden era'' of Pop III searches.

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astro-ph.GA 2026-07-01

Lyα escape persists in massive dusty galaxies at high redshift

by Rahul Rana, Julie L. Wardlow +4 more

Far-infrared observations of dust in Lyα emitters at z=2-6

Far-IR stacking of 4000 LAEs finds non-zero escape fractions even in AGN-hosting systems, implying clumpy dust allows ionizing photons to le

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The bright Ly$\alpha$ line is regularly used to identify high-redshift star-forming galaxies known as Ly$\alpha$ emitters (LAEs). However, Ly$\alpha$ is affected by resonant scattering and dust absorption making interpretation of its brightness challenging without additional observations. We use SCUBA-2, PACS and SPIRE data to investigate the far-infrared emission, Ly$\alpha$ escape fraction ($f{esc}$(Ly$\alpha$)) and infrared excess (IRX=LIR/LUV) in $\sim$4000 LAEs at z=2.2-6 from SC4K. Five LAEs, all hosting AGN, are individually detected with fluxes $S_{850}$ = 3.7-5.5 mJy at 850$\mu\mathrm{m}$. Stacking is used to probe the average emission from all individually undetected LAEs, though the stacks are undetected at all wavelengths (e.g. $S_{850}$ < 0.09 mJy; 3$\sigma$). We group the sample into bins of redshift, stellar mass, Ly$\alpha$ luminosity and AGN status. Most subsets are undetected but LAEs containing AGN and that have high stellar masses ($M_{\star} = 10^{10} - 10^{12}\, M_{\odot}$; including and excluding AGN) are detected at most wavelengths, suggesting that stellar mass and AGN heating may be enhancing the dust visibility. Individually detected LAEs and detected stacks have $f{esc}$(Ly$\alpha$)=1-7%, while all undetected stacks $\geq$ 10%. All LAEs together average over > 21% and display significant scatter, suggesting a clumpy ISM dust distribution. Non-zero $f{esc}$(Ly$\alpha$) in massive and AGN-hosting LAEs suggests ionizing photons may escape even from dusty galaxies, challenging the idea that dusty galaxies are poor leakers. Examination of the IRX-$\beta_{UV}$ relation shows LAEs have higher IRX than typical star-forming galaxies at similar redshifts. However, our detections tend to favour more massive, AGN-hosting systems and deeper observations are therefore needed.

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astro-ph.GA 2026-07-01

GPU code recovers barred galaxy densities and pattern speeds

by Hanyuan Zhang, David Chemaly +4 more

SchwarMAX: a GPU-friendly Schwarzschild orbit-superposition modelling framework

SchwarMAX builds full Schwarzschild models in one second on A100, enabling MCMC fits that match input profiles from N-body mocks.

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The Schwarzschild orbit-superposition method is a highly flexible dynamical modelling tool. It constrains the mass distribution of a galaxy using line-of-sight velocity and photometric observations. However, constructing such a dynamical model of a galaxy is computationally expensive. We present SchwarMAX, a new publicly available GPU implementation of the Schwarzschild orbit-superposition method. The GPU-native code is significantly faster than other implementations, with entire model construction taking around a second on GPU A100. Using SchwarMAX, we can explore the distributions of both baryonic and dark matter in a galaxy across a high-dimensional parameter space. We demonstrate its performance using mock integrated-field spectroscopic unit data generated from an N-body simulated barred galaxy. We explore the 12-dimensional space of disc, bar and halo parameters using Markov Chain Monte Carlo. The density profiles and the bar pattern speed of the galaxy are recovered with good accuracy. We show that the code can be applied to barred galaxies across a wide range of inclination angles and can be easily extended to other stellar systems, such as elliptical and dwarf galaxies.

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astro-ph.CO 2026-07-01

XRISM measures lowest turbulence yet in Abell 496 core

by Angie Veronica, Thomas H. Reiprich +10 more

The Quiescent Sloshing Core of Abell 496 with XRISM

Bulk velocity 69 km/s and dispersion 78 km/s indicate a dynamically quiet ICM despite prior cold fronts and radio activity.

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Gas motions provide insight into the dynamical history and physical processes within galaxy clusters. We investigate the kinematics of the ICM in the core of A496, a nearby, X-ray bright, strong cool-core cluster, using high-resolution data from the Resolve micro-calorimeter on board XRISM. We compared our measurement with other Resolve cluster core measurements and further compared our results with simulations and multiwavelength observations. From an optical redshift analysis, we found that the BCG is at rest with respect to the systemic velocity of the cluster. Despite multiple previously detected cold fronts and harboring a weak central radio source, Resolve observation shows that the core of A496 is dynamically quiescent. The ICM is moving with respect to the BCG with a LOS bulk velocity of $v_{\rm bulk}=-69_{-20}^{+25}\,\mathrm{km\,s}^{-1}$. We measured a turbulent velocity of $\sigma_{\rm v}=78_{-16}^{+18}\,\mathrm{km\,s}^{-1}$, the lowest value reported by the instrument on a cluster core to date. This value is in good agreement with the velocity dispersion of the H$\alpha$ filament in the core, which may indicate condensation of ICM in the wake of the radio bubble. Assuming isotropic turbulence, the ICM turbulent velocity corresponds to a subsonic 3D Mach number of $0.15_{-0.03}^{+0.04}$ and a non-thermal pressure fraction of $1.2_{-0.5}^{+0.6}\,\%$. The mechanical AGN feedback from the recent activity of the central radio source is estimated to contribute about 7-9% to the ICM heating. The 1D LOS bulk velocity from the SLOW constrained Universe simulation is consistent with the measured value, suggesting that AGN feedback has a negligible contribution. The A496 SLOW turbulent velocity, as in other reported Resolve--simulation comparisons, is higher, but remains within $1.5\sigma$ uncertainty. A496 may represent one of the most quiescent sloshing cores observed so far.

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astro-ph.GA 2026-07-01

Eddington ratio alone sets AGN outflow incidence and obscuration

by Carolina Andonie, Andrea Merloni +13 more

AGN radiative feedback as the main regulator of [O III] outflow activity and obscuration in X-ray AGN

Trends with accretion rate survive only when samples are matched on luminosity, pointing to radiation pressure rather than black hole mass.

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Large-scale ionised outflows and nuclear obscuration are fundamental manifestations of AGN activity, yet direct observational evidence linking these phenomena remains scarce. We use the eROSITA Final Equatorial Depth Survey, among the largest uniform optical spectroscopic datasets of X-ray AGN, to investigate how AGN accretion rate affects ionised outflow kinematics and X-ray obscuration. Our sample comprises 2.840 AGN at z<0.82 with high-quality SDSS spectra. Through optical spectral fitting, we measure Eddington ratios ($\lambda_{Edd}$) and [O III] emission-line kinematics, tracing ionised outflows. In addition, we use archival eROSITA X-ray spectroscopy with X-ray stacking analyses to constrain the obscuration of the sample, $N_H$. We find that (1) 35% of the entire sample hosts a [O III] outflows ($W_{80}>600$ km/s), with the outflow incidence increasing with the AGN luminosity from 15% at $L_{AGN}<10^{44}$ erg/s up to 60% at $L_{AGN}>10^{46}$ erg/s; (2) the outflow incidence increases with Eddington ratio from 29% at $\log \lambda_{Edd}<-2.3$ to 50% at $\log \lambda_{Edd}>-1.7$; and (3) the AGN obscuration decreases with Eddington ratio, as sources with $\log\lambda_{Edd}>-1.7$ are 5 times less obscured than lower Eddington ratios AGN. In addition, we find that 1% of the sample populates the "forbidden region" of the $N_H-\lambda_{Edd}$ plane, where the outflow incidence peaks at 52%, consistent with a short-lived feedback phase. Notably, when matching the Eddington ratios samples in AGN luminosity, these trends vanish, implying that radiation pressure drives changes in outflow activity and obscuration, while the black hole mass does not play a significant role. Our results are in agreement with AGN radiative feedback scenarios, where the Eddington ratio regulates the AGN environment by driving powerful, galaxy-wide outflows and shaping the amount of circumnuclear material.

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astro-ph.GA 2026-07-01

Gaia DR3 census identifies 1256 Stellar Snakes near Sun

by Xiang-Ming Yang, Ju-Yong Zhang +1 more

The Stellar "Snake"-V: the census within 3 kpc in the Solar Neighborhood

Catalogue of 802489 stars in coherent 9D associations offers foundation for studying Milky Way star formation hierarchies.

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We present a Gaia DR3 source-level census of \emph{Stellar Snake} complexes within 3\,kpc of the Sun. We define a Stellar Snake as a mutually coherent association of two or more stellar overdensities, characterised by consistent positions, kinematics, orbital invariants, ages, and chemical properties, rather than as a single gravitationally bound object. Moving beyond catalogue-driven searches seeded by known open clusters, our framework operates directly on individual Gaia sources to recover extended, low-density substructures and interconnecting stellar bridges. The multi-stage pipeline extracts statistically significant, non-overlapping base nodes, infers homogeneous parameters using a PointNet point-cloud regressor, and links these nodes into large-scale macro-structures across a 9D space spanning positions, tangential velocities, radial velocity, age $\log t$, and orbital integrals $(E,L_Z)$. After FoF-topology cross-validation and boundary resolution, the final catalogue contains 1,256 Stellar Snake candidates comprising 802,489 unique member-star entries in 5,491 final base nodes selected from a 9,909-node input pool. Derived parameters are validated against external open-cluster catalogues and spectroscopic benchmarks. To quantify structural coherence, we introduce a graph-relation Snake Reliability Index (SRI), coupled with a peripheral-branch diagnostic and Gold/Silver/Bronze quality flags. At the population level, the census shows a broad age--metallicity pattern, a declining upper envelope of member-star entries toward older ages, and a projected association between young Snake nodes, nearby spiral-arm loci, and the Radcliffe Wave. This homogeneous inventory provides an observational foundation for probing the formation, coherence, and dynamical evolution of hierarchical stellar complexes in the Milky Way.

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astro-ph.GA 2026-07-01

Gaia data yields 6 confirmed dual quasars

by Qihang Chen, Zizhao He +4 more

Search for Quasar Pairs with {it Gaia} Astrometric Data. III. Discovery of 9 dual and projected quasars

Spectroscopy of 11 candidates finds pairs including one at z~3.1 and shows how photometric redshifts cut contamination

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We report the low-resolution long-slit spectroscopic observations and confirmations of 11 quasar pair candidates, which are selected from the MGQPC catalog presented in the first paper of our series work (hereafter, Paper-I) and the early version of this catalog. The spectroscopic follow-up was carried out with 5 spectrographs equipped on 3 telescopes, and the major discoveries include 6 dual quasars and 3 projected quasars. One of the dual quasars has a high redshift of $\sim$ 3.1. The LQ hypothesis of 3 dual quasars cannot be completely ruled out. We investigated the reason why previous spectroscopic surveys missed several new quasars. We discussed a projected quasar with a wide-separation lensing configuration, as well as two quasar-star projections that mimic the configuration of lensed quasars. The photometric redshifts for the 11 observed candidates were extracted from the second paper of our series work (hereafter, Paper-II) to illustrate their positive role in mitigating contamination from projected quasars and quasar-star projections. We also reviewed and discussed the confirmation strategies for dual and lensed quasar candidates, and outlined future confirmation strategies for them in the context of the era dominated by large-scale spectroscopic and imaging surveys.

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astro-ph.GA 2026-07-01

Post-starburst galaxies hide extra asymmetry at z>1

by David T. Maltby, Omar Almaini +10 more

The multiwavelength structure of post-starburst galaxies at 0.5 < z < 3 with JWST PRIMER: compact morphologies and residual disturbances

JWST data show they are compact with little wavelength variation yet retain more residual disturbances than passive galaxies at high mass an

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We investigate the multi-wavelength structure of recently quenched post-starburst (PSB) galaxies at 0.5 < z < 3, using photometrically selected samples from the Ultra Deep Survey (UDS). Leveraging deep eight-band JWST/NIRCam imaging from the PRIMER programme, we analyze ~120 PSBs across the rest-frame optical-to-near-infrared, and compare with a reference sample of ~3000 passive and star-forming galaxies. Structural parameters (effective radius Re and Sersic index n) are derived independently in each waveband, and reveal that PSBs exhibit minimal structural variation with wavelength, indicating negligible stellar population age gradients or internal dust obscuration. We confirm that PSBs follow the established redshift-mass trends: at z > 1, massive PSBs (M* > 10^10 Msun) are compact spheroids resembling massive passive galaxies, albeit significantly more compact, whereas at 0.5 < z < 1, PSBs are typically low-mass (M* < 10^10 Msun) compact, disc-dominated systems akin to low-mass passive discs. Furthermore, for the first time, we systematically quantify disturbance indicators (residual flux fraction RFF, asymmetry, residual asymmetry) across a large PSB sample. At all masses, PSBs exhibit low RFF and asymmetry values comparable to passive systems and consistent with smooth, largely undisturbed morphologies. However, at z > 1, massive PSBs (M* > 10^10.25 Msun) show enhanced residual asymmetry relative to the passive population, indicating a previously unrecognized level of structural disturbance masked beneath a smooth stellar distribution. These results suggest that, while structural transformation is largely complete by the PSB phase, residual disturbances persist at high redshift, supporting a scenario in which rapid quenching proceeds via two distinct pathways: highly disruptive events (e.g. major mergers) at high z and high mass, and comparatively gentle processes at later times.

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astro-ph.GA 2026-07-01

LRD density drops gently from z~5 peak to z~2

by Shrriya Kapoor, Jorryt Matthee +11 more

Little Red Dots at z~2 in EIGER reveal a gentle decline with respect to their peak number density at z~5

Spectroscopic sample shows they comprise under 3% of AGNs at z=1.9-2.5, milder than photometric surveys reported.

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We report the discovery of a sample of little red dots (LRDs) at $z \approx 2$ identified from deep JWST/NIRCam imaging and wide-field slitless spectroscopy over $140$ arcmin$^2$ from the EIGER survey. With an improved blind broad-line identification algorithm, we select 19 sources at spectroscopic redshifts $z = 1.55-3.18$ identified via rest-frame near-infrared lines (Paschen-$\beta$, HeI+Pa$\gamma$ and OI). Based on a range of spectro-photometric criteria, we classify five of these sources as LRDs and the other 14 as classical active galactic nuclei (AGNs). This classification is corroborated by some X-ray detections among the AGNs. Classical AGNs dominate the number counts above optical luminosities M$_{5100}<-22.5$, whereas the LRD fraction among broad-line sources reaches 100 % at M$_{5100}\approx-20$. The LRDs span the range in Balmer break strengths seen in the higher redshift populations. Blue-shifted HeI absorption is detected in the two reddest sources. The HeI/Pa$\gamma$ ratio cleanly separates LRDs from classical AGNs and seems to anti-correlate with Balmer break strength, likely tracing HeI self-absorption at higher gas column densities. Our LRD sample has a similar optical luminosity range as their high-redshift counterparts, corresponding to black hole masses of $\sim10^{6}$ M$_{\odot}$ at the Eddington luminosity. We measure LRD number densities of $\approx 7\times10^{-6}$ cMpc$^{-3}$ at $z = 1.9-2.5$, which indicates that LRDs represent $\lesssim 3$ % of the AGN population at these epochs. Our results confirm the previously reported decline in the LRD number density with respect to $z \approx 5$ based on photometric surveys, although we find the decline to be more gentle than earlier emphasized.

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astro-ph.GA 2026-07-01

Stars heat when migrating inward in Milky Way galaxies

by Cecilia Steel, Andrew Wetzel +4 more

Hot or Cold? Radial Redistribution of Stars in FIRE Simulations of Milky Way-Mass Galaxies and the Asymmetry of Inward versus Outward Migrators

FIRE simulations find inward migrators gain eccentricity while some stars cool to circular orbits; overall migration is rarely cold.

abstract click to expand

Stars can radially redistribute (migrate) within galactic disks. The degree to which this occurs as dynamically `cold' (preserves orbital eccentricity) or `hot' (increases eccentricity) remains debated. Many models presume that radial redistribution occurs primarily via cold torquing, resulting in changes in angular momentum without dynamical heating. We test the net dynamical heating associated with redistribution over stellar lifetimes using the FIRE cosmological zoom-in simulations of 12 Milky Way-mass galaxies. We select star particles today that underwent significant changes in orbital angular momentum, j_phi, since birth. We investigate net changes in their orbital eccentricity, e, and we quantify the `cold-torqued' fraction of star particles with |Delta j_phi/j_phi,birth| > 0.2 that preserved eccentricity (|Delta e| < 0.1) since birth. The direction of radial redistribution is most critical: outward-migrating stars experienced smaller net changes in eccentricity, whereas inward-migrating stars almost always heat since birth. For stars born on near-circular orbits (e_birth < 0.2), the cold-torqued fraction decreases rapidly with age today and is generally < 50% at ages >~2 Gyr. Stars born on moderately eccentric orbits (e_birth ~ 0.4) are the most likely to preserve their birth eccentricity. However, the cold-torqued fraction is higher in earlier-forming and/or dynamically-colder disks. Significantly, we identify a population of stars that dynamically `cooled', decreasing in eccentricity since birth: this is the primary way that stars end up on near-circular orbits today. Overall, a star's migration direction, its e_birth, and its age primarily determine whether it was dynamically heated, cooled, or unchanged. In general, radial redistribution in FIRE is typically not cold between birth and today.

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astro-ph.GA 2026-07-01

Quiescent galaxies cluster more at fixed halo mass

by Louise Paquereau, Clotilde Laigle +30 more

COSMOS-Web: does halo mass alone shape the clustering of star-forming and quiescent galaxies?

COSMOS-Web data show 0.5-1 dex excess persists from z=5 with conformity to z=2, so halo mass alone does not set clustering.

abstract click to expand

While stellar mass correlates strongly with halo mass, it remains unclear whether halo mass alone governs galaxy star-formation activity, or whether secondary halo properties and environment also play a role. We investigate these effects beyond halo mass by measuring the auto- and cross-correlations of star-forming and quiescent galaxies in the COSMOS-Web survey from $z = 5$ to the present day. To isolate environmental contributions, we introduce a method that matches the halo mass distributions of both populations using the UniverseMachine model. We find that quiescent galaxies remain more strongly clustered than star-forming systems by at least $0.5-1$ dex at all redshifts, even after controlling for halo mass. At $z \le 2$, this excess clustering increases towards lower stellar masses, with the most clustered objects being $\log(M_\star/{\rm M}_\odot) \le 9.5$ quiescent galaxies. This points to environmental quenching significantly affecting low-mass galaxies at $z \le 2$, likely driven by ram-pressure stripping or the suppression of cold gas accretion, as these objects show disky morphologies. Cross-correlations further reveal one-halo conformity up to $z \simeq 2$: low-mass (or satellite) quiescent galaxies are more strongly clustered around massive (or central) quiescent galaxies than around star-forming centrals of the same halo mass. This signal may arise from quenching mechanisms affecting both centrals and satellites, correlated assembly histories prior to infall, or dependencies on secondary halo properties. Both environmental quenching and conformity appear to vanish between $z \simeq 5$ and $2$. Together, these results challenge the common assumption that clustering and star-formation activity depend solely on halo mass.

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astro-ph.GA 2026-07-01

Roberts Quartet assembles through interactions in under 500 million years

by Saili Keshri, Sudhanshu Barway +2 more

Caught in the act: interaction-driven evolution in the nearby compact galaxy group Roberts Quartet (SCG0018-4854)

Spatially resolved maps show disturbed motions and recent gas exchange, making the group a local template for rapid galaxy assembly.

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We present a spatially resolved multiwavelength study of the compact galaxy group Roberts Quartet (RQ, SCG0018-4854), aimed at understanding interaction-driven galaxy evolution in a dense environment. RQ comprises of four galaxies (NGC 87, NGC 88, NGC 89, and NGC 92) that span a range of masses and evolutionary states. Using UV-to-IR data from GALEX, DECaLS, MUSE/VLT (IFU), VISTA/VIRCAM, 2MASS, and WISE, we investigate the interplay between kinematics, star formation, and stellar populations across the group. The spatially resolved analysis reveals disturbed stellar and gas kinematics, enhanced turbulence, and asymmetric structures in all members, consistent with repeated gravitational interactions. The most massive galaxy, NGC 92, exhibits prominent tidal features, a bar, and ring-like star-forming structures, indicative of interaction-driven gas inflows. Another massive member, NGC 89, shows suppressed star formation and signatures of AGN-driven feedback, while the lower-mass galaxies NGC 88 and the dwarf galaxy NGC 87 display enhanced star formation and kinematic decoupling between stellar and gas component consistent with recent gas accretion. Combining UV age estimates with non-parametric star formation histories, we constrain the recent interaction timescale of the group to <= 500 Myr, whereas the crossing timescale is 424 Myr. These results indicate that RQ is a dynamically young system undergoing ongoing assembly, where interactions, gas exchange, and feedback processes are actively shaping galaxy evolution. The dynamical complexity of the group further suggests that its present configuration may involve more than four progenitor components. In this context, RQ provides a nearby analogue of compact, rapidly evolving groups observed at high redshift by recent JWST observations, offering a resolved view of the physical processes governing galaxy assembly in the early Universe.

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astro-ph.GA 2026-07-01

ELT SHARP will map z>9 Lyman-alpha nebulae at 150 pc scales

by Susanna Bisogni, Giustina Vietri +6 more

Unveiling the Cosmic Dawn with SHARP: Probing extended Lyman-α nebulae in a Universe less than 600 Myr old

First views of gas structures around early quasars less than 600 million years after the Big Bang.

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The existence of luminous quasars just a few hundred million years after the Big Bang challenges our understanding of both black hole growth and galaxy formation and evolution. These objects harbour supermassive black holes exceeding a billion solar masses (M$_{BH} > 10^{9} M_{\odot}$) by redshift $z\sim 6.5$-$7.5$, powered by extreme gas accretion. At the same time, their host galaxies are also undergoing intense star formation, consuming gas at the rate of hundreds of solar masses per year. Characterising the circumgalactic medium (CGM) and intergalactic medium (IGM) surrounding high-redshift quasars becomes an essential tool to understand the conditions that enable the rapid formation and evolution of these extreme sources. While in the last decades spatially resolved observations in the optical band have targeted CGM through Ly$\alpha$ nebulae surrounding $z \sim 2-6$ quasars, current instrumental limitations hamper observations of high-z ($z>8$) quasars that will be discovered by Euclid/Roman/LSST surveys. Despite the large fraction of neutral hydrogen at the epoch of reionisation, in the last decade several surprising Ly$\alpha$ detections have been obtained from sources deep in the epoch of reionisation. The unprecedented collecting area of ELT, coupled with the resolution and wavelength coverage of SHARP, specifically VESPER, will enable us to map for the first time $z>9$ Ly$\alpha$ emission down to the structures of size $\sim$150 pc, while simultaneously capturing their large-scale structure up to 100 kpc for the first time at this redshift. This will allow a major and long-awaited step forward in the exploration of quasars and galaxies formation and evolution deep in the epoch of reionisation.

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astro-ph.GA 2026-07-01

SKAO to trace AGN gas flows in hundreds of galaxies

by Filippo M. Maccagni, Vincenzo Mainieri +9 more

AGN Feeding & Feedback Over the Galactic Scales

Reaching sensitivities of 10^19 cm^-2 in HI at arcsecond scales to link nuclear episodes with galactic star formation.

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Active Galactic Nuclei (AGN) are key drivers of galaxy evolution, triggered by cold gas accreting onto a super-massive black hole. However, the processes regulating this gas accretion (feeding) and how AGN alter the interstellar medium to affect star formation (feedback) remain poorly understood. A major observational challenge is the vast range of spatial scales involved: AGN fuelling and jet-ejection occur over the sub-pc scales, while AGN feedback shocks and heats the ISM preventing star formation over the galactic and circum-galactic scales. Moreover, it is unclear how short stochastic AGN episodes are connected with the long timescales of gas accretion and star formation. In this manuscript, we illustrate how SKAO will provide the unprecedented opportunity to solve the observational limitations of AGN feeding and feedback studies by observing hundreds of nearby AGN down to low radio powers ($10^{21}$ W Hz$^{-1}$). Simultaneous SKA-Low and Mid observations of nearby galaxies will trace the thermal emission associated with star formation and AGN feedback and the synchrotron emission of their jets of relativistic plasma. These broad-band radio observations enable the detailed characterisation of the AGN duty-cycle, unravelling the time-scales of the nuclear activities. Reaching in 10 hours neutral atomic hydrogen (HI) column density sensitivities $\sim 10^{19}$ cm$^{-2}$ at arcsecond resolution, SKA AA4 observations will trace the typical low column density of HI gas in AGN inflows and outflows, to understand the impact AGN feedback over the full galaxy and trace fuelling processes from the environment onto the SMBH. Combining SKA with mm, sub-mm and optical Integral Field Spectrographic observations at comparable arcsecond resolution will provide an exhaustive understanding of the link between multi-phase AGN feeding and feedback processes and star formation.

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astro-ph.GA 2026-07-01

Gaia revises Sh2-106 distance to 1.65 kpc and raises outflow energy 6.5 times

by Sergio A. Dzib

Distance to Sh2-106 from Gaia DR3 and its embedded radio population: implications for a candidate explosive outflow

Larger distance aligns the candidate explosive event with Orion BN/KL energetics at an older dynamical age near 3500 years.

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Sh2-106 has recently been proposed as a candidate explosive molecular outflow (EMO), but the physical interpretation of the region depends critically on its distance. Published estimates span a wide range, leading to large uncertainties in the inferred size, energetics, and evolutionary timescale of the system. Using {\it Gaia} DR3 astrometry, we identify a kinematically coherent stellar population associated with Sh2-106 and derive a cluster parallax of $\varpi_{\rm corr}=0.607\pm0.013$\,mas, corresponding to a distance of $1.65\pm0.04$\,kpc. This value is significantly larger than the commonly adopted extinction-break estimate of 1.09\,kpc. At this revised distance, the inferred kinetic energy of the expanding ionized nebula increases by a factor of $\sim6.5$, reaching $E_{\rm exp}\simeq1.3\times10^{48}$\,erg and placing Sh2-106 in the same order-of-magnitude energetic regime as the Orion BN/KL explosive event, although at a substantially older dynamical age ($\sim3500$\,yr). Archived 5.8\,GHz Karl G. Jansky Very Large Array observations reveal ten compact radio sources in the central region, identifying embedded stellar objects that are suitable for future multi-epoch radio astrometry. No unambiguous high-velocity stellar ejecta are detected in {\it Gaia} DR3, although S106\,IR shows a modest peculiar transverse velocity of $\sim5$\,km\,s$^{-1}$ relative to the cluster centroid. The Gaia-based cluster distance, therefore, significantly revises the physical scale and energetics of Sh2-106 and provides the observational framework required to test whether the region represents an older analogue of the Orion BN/KL dynamical disintegration or a distinct explosive phenomenon.

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astro-ph.IM 2026-07-01

Ghosts affect 0.57% of LSSTCam focal plane

by Aashay Pai, Alex Drlica-Wagner +5 more

In Situ Measurements of the Reflectances of the LSSTCam Optics and Assessing the Impact of Optical Ghosts

Simulations tuned to commissioning data and reflectance measurements quantify reflection artifacts in the camera.

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Optical ghosts are image artifacts caused by successive reflections of light between optical surfaces such as lenses, filters, and detectors. These artifacts are unavoidable due to the nonzero reflectances of optical elements and are a major source of contamination for low-surface-brightness science. We use optical ray tracing simulations tuned to observations from LSST Commissioning to quantify the impact of optical ghosts on the LSST data. In particular, we find that ~0.57% of the LSSTCam focal plane is impacted by optical ghosts when averaged across all bands. We also use data from the Collimated Beam Projector to measure the reflectances of various optical elements, generally confirming estimates of ~2% from the systems engineering throughput predictions.

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astro-ph.GA 2026-07-01

SKA-VLBI to map HI at parsec scales in radio galaxy jets

by Mamta Pandey-Pommier

Uncovering neutral Hydrogen clouds in Radio Galaxies in the SKA era

Milliarcsecond resolution will track atomic gas from nuclei to jet-ISM sites in molecular-rich AGN.

abstract click to expand

AGN feedback driven by radio jets plays a key role in regulating the cold ISM of galaxies. Neutral hydrogen traced through the H1 21-cm line provides a powerful probe of the kinematics, distribution, and physical conditions of cold gas in the central regions of AGN. Previous observations have detected H1 column densities down to $\sim10^{20}$ cm$^{-2}$, but typically at arcsecond-scale resolution, inhibiting the characterization of small-scale H1 gas clouds and their connection to molecular gas reservoirs and sites of jet-ISM interaction. High-resolution H1 imaging is therefore required to determine whether the atomic gas is associated with circumnuclear structures, jet-driven outflows, compressed gas layers, or fragmented cold clouds embedded within a disturbed multiphase ISM. In this chapter, we focus on molecular gas-rich radio AGN hosting large-scale jets and exhibiting strong interactions between the radio plasma and the surrounding ISM, where atomic, molecular, and ionized gas coexist. These systems provide ideal laboratories for investigating the spatial distribution and kinematics of H1, constraining the impact of radio jets on the cold gas, and determining whether the gas is associated with inflowing, outflowing, or otherwise disturbed components. SKA-VLBI will deliver milliarcsecond-scale imaging and $\mu$Jy-level sensitivity, resolving H1 gas clouds on parsec scales across extended radio structures. This capability will enable detailed constraints on the location, morphology, and kinematics of atomic gas from the nuclear regions to kiloparsec-scale jet-ISM interaction sites. Combined with molecular gas observations at other wavelengths, these measurements will provide a comprehensive view of the jet-ISM interactions, the impact of AGN-driven feedback, and the role of cold gas in galaxy evolution.

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astro-ph.GA 2026-07-01

Eight clusters show radial shifts under 0.5 kpc

by Remziye Canbay, Deniz Cennet Ç{i}nar +5 more

Chemo-dynamical Analysis of Eight UBC Open Clusters

Orbital tracing of distant open clusters finds modest displacements, pointing to mild redistribution in the thin disk.

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We present a comprehensive chemo-dynamical analysis of eight open clusters selected from the UBC catalog using Gaia DR3 data. These clusters are located at heliocentric distances of ~2-5 kpc, probing regions of the Galactic disk beyond the solar neighborhood. Cluster membership is determined using the UPMASK algorithm, while structural parameters are derived from radial density profiles through King model fitting combined with MCMC sampling. Their structural parameters reveal diverse internal configurations, from diffuse to moderately concentrated systems. Fundamental astrophysical parameters (extinction, distance, metallicity, and age) are obtained via Bayesian isochrone fitting based on PARSEC models. The clusters span a wide age range (~20 Myr to ~5 Gyr) and show a broad metallicity distribution (-0.34 <= [Fe/H] (dex) <= +0.25). Orbital analysis based on backward integrations shows that all clusters follow nearly circular orbits (e ~ 0.03-0.09) with low vertical distances from the Galactic plane (Zmax < 0.4 kpc), confirming their membership in the Galactic thin disk and dynamically cold kinematics. Comparison between inferred traceback orbital radii and present-day guiding radii indicates modest radial displacements, with Delta R < 0.5 kpc for the UBC sample. These offsets are consistent with mild radial redistribution expected for young, dynamically cold open clusters rather than strong radial migration. The results suggest that radial migration should be considered when interpreting the present-day spatial and chemical distribution of these clusters, although the inferred migration amplitudes remain moderate. Our results demonstrate that relatively distant open clusters can be characterized with high precision using Gaia DR3 data and that mild radial redistribution should be considered when interpreting the present-day distribution of stellar populations in the Galactic disk.

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astro-ph.GA 2026-07-01

80 hours of ELT time can map gas flows in 60 galaxies across 10 dense structures at z~2

by M. Polletta, G. De Lucia +2 more

Fueling and feedback mechanisms at the nodes of the cosmic web

The resulting kinematics and star-formation maps would show which processes quench galaxies as protoclusters become virialized clusters.

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The environment plays a key role in shaping how galaxies form and evolve. Galaxies in dense nodes of the cosmic web are thought to grow and quench earlier, and faster and become more massive than those in the field. To understand the physical drivers of this environmental effect, we must probe the most crowded regions of the Universe at the epoch when growth was at its peak and the transition to quiescence was triggered, around 10 billion years ago (z ~ 2). This period saw the downturn of the cosmic star-formation and black-hole accretion histories, the quenching and morphological transformation of massive galaxies, and the virialisation of the first clusters. Several processes might be at play: stellar and AGN feedback, reduced gas accretion, disk instabilities, morphological quenching, interactions, and ram-pressure stripping. The ELT/SHARP instrument, with its sensitivity, spectral resolution, wavelength coverage, and multiplexing capabilities over a wide field, is ideally suited to study these mechanisms by targeting multiple members of dense structures simultaneously. Cluster and protocluster cores at z ~ 2 span roughly 1 arcmin and host about ten massive (Mstar > 10^10.5 Msun) galaxies. VESPER can deliver spatially resolved gas and stellar kinematics, map recent and past star formation, identify companions, inflows, outflows, shocks, and AGN activity for the most massive core members. With 80 hr of VESPER time, we can obtain this type of data for about 60 galaxies selected from the densest regions of five clusters at 1.5 < z < 1.7 and five protoclusters at 2 < z < 2.5 spanning the evolutionary phases of maximal growth and rapid decline. Such a sample would permit to trace the evolution from protoclusters to virialised clusters and identify the environmental processes responsible for their rapid transformations.

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astro-ph.GA 2026-07-01

Galaxy overdensity at z=5.945 is 0.4 dex more metal-poor than peers

by Zihao Li, Koki Kakiichi +25 more

Possible chemical signatures of first-star enrichment in a very metal-poor galaxy overdensity near the end of reionization

17 members average 3 percent solar metallicity near an absorber with first-star-like carbon and silicon ratios.

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The first generation of stars, known as Population III (Pop III), formed from primordial gas consisting solely of hydrogen and helium and is believed to have emerged only a few hundred million years after the Big Bang. Detecting the chemical enrichment of metal-poor circumgalactic gas offers a promising way to trace the enrichment signature of Pop III stars. Along the sightline to the quasar SDSS J0100+2802, a metal absorber at $z = 5.945$, showing over-abundant carbon and silicon compared to solar, has been reported to be consistent with the enrichment pattern of Pop III stars. With the James Webb Space Telescope, we report the discovery of an unusually metal-poor galaxy overdensity of 17 members (mean metallicity $\approx 3\%$ solar) near this metal absorber, which is $\sim 0.4$ dex more metal-poor than coeval galaxies in similarly overdense environments. This less chemically evolved system may have provided favorable conditions for preserving the absorption signatures of Pop III enrichment. The cross-correlation of the metal absorber and the surrounding galaxies indicates a minimum dark matter halo of $\log(M_{\mathrm{h,min}}/M_{\odot})=10.68^{+0.93}_{-1.72}$, consistent with late-time Pop III formation at the outskirts of atomic hydrogen cooling halos.

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astro-ph.CO 2026-07-01

One percent PBHs change ULDM soliton participation by twenty percent

by Xing-Yu Yang

Ultralight dark matter mixed with primordial black holes

Continuum background effect dominates while discrete fluctuations take 10 billion years to act on galactic halos.

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Dark matter candidates span many orders of magnitude in mass, from ultralight bosonic fields to massive compact objects. In this work, we connect these two extremes by investigating ultralight dark matter (ULDM) mixed with primordial black holes (PBHs). We study mixed ULDM-PBH halos by separating the continuum PBH contribution from the shot-noise fluctuation generated by discrete PBHs. The continuum contribution enters the averaged Schr\"odinger-Poisson background, while the discreteness contribution is treated as a perturbation that induces ULDM eigenmode transitions and soliton heating. The two contributions have distinct parametric dependencies: continuum effects scale with PBH fraction, whereas discreteness-driven transition rates scale with the product of PBH fraction and individual PBH mass in the perturbative regime. For a fiducial mixed halo with ULDM particle mass $10^{-22}\,\mathrm{eV}$, virial mass of order $10^{10}\,M_{\odot}$, and PBH fraction $1\%$, the continuum PBH component modifies the background density, gravitational potential, and low-lying ULDM eigenvalues only at the sub-percent level. Nevertheless, this percent-level continuum PBH contribution produces a tens-of-percent response in the coherent soliton region, changing the radial mode participation by about $20\%$. For stellar-mass PBHs, the discrete shot-noise fluctuation induces extremely slow ULDM mode transitions, with the fastest low-lying multiplet transition having a timescale of order $10^9\,\mathrm{Gyr}$ for solar-mass PBHs. In this regime, the leading PBH effect is the continuum contribution, while discrete PBH shot noise is dynamically negligible on galactic timescales.

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astro-ph.GA 2026-07-01

SHARP reaches stellar gradients to 2Re in 20h at z<2.5

by A. Gargiulo, C. Mancini +7 more

A big step forward with SHARP: spatially resolved stellar population properties in passive galaxies at z > 1.5

Feasibility study shows ELT instrument maps population properties in early passive galaxies out to twice the effective radius.

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Understanding when and how massive quiescent galaxies (log(M*/Msun) > 10.5) assembled their stellar mass and quenched remains a central challenge in galaxy evolution. Spatially resolved stellar population measurements at z > 1.5 offer a uniquely powerful avenue to address this problem, as they can provide information on the radial variations in stellar age, metallicity, and enrichment histories in passive galaxies as they first emerge. In this work, we present a feasibility study quantifying the transformative capabilities of the proposed IFU SHARP/VESPER at the ELT for performing such radial mapping of stellar population gradients in passive galaxies at 1.5 < z < 3. Using the COSMOS-Web catalogue, we define a realistic population of massive quiescent systems at 1.5 < z < 3 and model representative compact and extended galaxies across this redshift range. Through detailed simulations with the official SHARP ETC, we derive the exposure times required to reach S/N = 10-15 per resolution element at key rest-frame optical wavelengths. Our results show that SHARP will routinely measure stellar population gradients out to 2Re for the majority of the population at z < 2.5 with integrations of about 20h, and that will reach at least Re in about 30h at z = 3. Thanks to MORFEO's MCAO and to its spatial resolution of 30mas SHARP/VESPER will also resolve the inner < 1kpc at all redshifts considered, enabling for the first time, direct tests of quenching mechanisms linked to central mass build-up, bulge growth, and structural transformation. These findings demonstrate that SHARP/VESPER will open an entirely new observational window on the early evolution of massive quiescent galaxies, providing, for the first time, statistically meaningful, spatially resolved stellar population constraints during the epoch when their stellar cores were assembled.

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astro-ph.GA 2026-07-01

ALMA maps reveal gas variations across NGC 1068 disk and ring

by Bin Jia, Serena Viti +2 more

Physical and Chemical Conditions of Molecular Gas in NGC 1068: The nuclear feedback in the circumnuclear disk and starburst ring

Bayesian analysis of multiple molecular lines shows radial and azimuthal changes in density, temperature, and cosmic-ray ionization.

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Molecular gas in galaxies is shaped by both star formation and active galactic nuclei. In NGC 1068, the circumnuclear disk and the starburst ring offer a nearby case to study these effects with many molecular tracers. Earlier work has shown strong outflow activity and complex chemistry, which motivates the use of methods that combine radiative transfer with time-dependent chemistry. Our aim is to map the physical conditions across the circumnuclear disk and the starburst ring of NGC 1068 and to test whether the nuclear outflow influences the molecular gas in the ring. We also examine whether the heating or the quiescent cloud scenario better matches the observations. We use archival ALMA observations obtained in Bands 3, 4, and 5, covering molecular species including HCN, HCO+, HNC, CS, CN and C2H. All data cubes are convolved to a common resolution of 0.8" and are sampled into 56 pc hexagons with a signal-to-noise threshold of three. We perform hierarchical Bayesian inference that links a non-LTE radiative transfer module SpectralRadex with chemical modelling. To make the analysis efficient, we replace direct UCLCHEM calculations with a neural network emulator trained on a large model grid. Sampling is done with Nautilus. We also compare our results with previous studies that used RADEX and UCLCHEM for selected regions. The emulator reproduces the UCLCHEM abundances with low error and allows inference at modest computational cost. We find clear radial and azimuthal variations in gas density, temperature, column density, and cosmic-ray ionization rate.

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astro-ph.GA 2026-07-01

Stacked JWST spectra show rising electron density in early galaxies

by Shihong Liu, Yu Rong

Electron Densities of Typical Low-Mass Galaxies at z~2-7 from Stacked JWST/NIRSpec Spectra

Low-mass galaxies average 381 cm^{-3} at z=5-7 versus 100-150 cm^{-3} at z=2-5, measured via [SII] ratios.

abstract click to expand

Direct electron-density measurements at high redshift are usually limited to galaxies with individually strong density-sensitive doublets, and therefore may not trace the average interstellar medium of ordinary low-mass galaxies. We stack public JWST/NIRSpec medium-resolution spectra from the DAWN JWST Archive to measure [SII]-based electron densities $n_e$ for low-mass galaxies at $2<z<7$. The accepted stacks yield $n_e\simeq100$--$150\ {\rm cm^{-3}}$ at $2<z<5$ and $n_e=381^{+104}_{-89}\ {\rm cm^{-3}}$ at $5<z<7$, corresponding to an evolution $n_e=n_{e,0}[(1+z)/(1+2.3)]^\alpha$ with $n_{e,0}=76^{+22}_{-23}\ {\rm cm^{-3}}$ and $\alpha=1.88^{+0.60}_{-0.64}$. A mass-matched stacking test gives a consistent rising trend, indicating that the increase is not driven solely by changing stellar-mass distributions. Individually measurable galaxies with both [SII] components detected at ${\rm S/N}>5$ have a higher normalization, $n_{e,0}=211^{+36}_{-31}\ {\rm cm^{-3}}$, showing that individual-doublet samples select a denser subset. Stacking archival JWST spectra therefore provides a direct route to measuring the average gas density of low-mass galaxies below the individual-doublet detection threshold.

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astro-ph.GA 2026-07-01

SKAO traces cold gas absorption from z=0 to beyond z=6

by Elizabeth K. Mahony, Neeraj Gupta +13 more

Tracing Cold Gas in Absorption Across Cosmic Time with the SKA

Wide frequency coverage and sensitivity enable atomic and molecular gas studies at every cosmic epoch.

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Observing the 21-cm HI line in absorption provides a powerful means of tracing the cold neutral gas in normal and active galaxies across cosmic time. The frequency coverage and sensitivity of SKAO will allow us to detect HI in absorption from z = 0 to beyond z = 6, enabling the characterisation of the properties of cold gas in and around galaxies at all epochs. This chapter summarises recent advances in absorption-line studies, lessons learned from precursor surveys, and updates the science case presented in Kanekar and Briggs (2004) and Morganti et al. (2015), focusing on the capabilities enabled by the SKA design baseline, Array Assembly 4 (AA4). We expand on these earlier works by presenting new opportunities to simultaneously search for OH 18-cm absorption, an efficient tracer of diffuse molecular gas that complements the atomic gas traced by HI absorption, as well as the need for sub-arcsecond scale spectroscopic imaging and multi-wavelength data from large surveys. These advances will allow SKAO absorption surveys to address key questions surrounding the fuelling and feedback cycles of AGN and the evolution of the cold neutral gas across cosmic time.

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astro-ph.GA 2026-07-01

FASHI survey fits HI mass function to single Schechter form

by Chuan-Peng Zhang (NAOC), Ming Zhu +9 more

The FAST All Sky HI Survey DR2: the FASHI Catalog and the HI Mass Function

Parameters are log M* = 9.89, alpha = -1.31; cosmic HI density is 4.71e-4 from 109000 sources.

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The FAST All Sky HI Survey (FASHI) conducted with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) has mapped $\sim 19500\,\mathrm{deg}^2$ of the sky north of DEC $= -14^{\circ}$, detecting $156411$ extragalactic HI sources at $z< 0.09$ with a median sensitivity of $0.57\,\mathrm{mJy}\,\mathrm{beam}^{-1}$ at a velocity resolution of $6.4\,\mathrm{km}\,\mathrm{s}^{-1}$. The survey achieves unprecedented depth and area coverage, significantly improving upon previous single-dish surveys. Through a detailed completeness analysis that accounts for the survey's non-uniform sensitivity and line-width dependence, we construct a robust HI mass function (HIMF) using a completeness-corrected sample of over $109000$ sources. The HIMF is robustly constrained down to $M_{\mathrm{HI}}\sim 10^{6.2}\,M_{\odot}$. When systematic uncertainties are included, the HIMF is well described by a single-Schechter function with a characteristic mass $\log (M_{*} / h_{70}^{-2}M_{\odot}) = 9.89\pm 0.02$, low-mass end slope $\alpha = -1.31\pm 0.02$, and amplitude $\phi_{*} = (6.38\pm 0.49)\times 10^{-3}\,h_{70}^{3}\,\mathrm{Mpc}^{-3}\,\mathrm{dex}^{-1}$. The derived cosmic HI density is $\Omega_{\mathrm{HI}} = (4.71\pm 0.03_{\mathrm{stat}}\pm 0.40_{\mathrm{sys}})\times 10^{-4}\,h_{70}^{-1}$. FASHI provides the most extensive and sensitive HI catalog to date, establishing an important benchmark for studies of gas accretion, galaxy evolution, and large-scale structure in the local universe.

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astro-ph.GA 2026-07-01

Linear matrix method extended to L=0 edges in stellar disks

by Evgeny V. Polyachenko, Ilia G. Shukhman

A generalized linear matrix method for normal modes in collisionless stellar disks

Boundary-integral terms keep matrix size fixed while computing m=2 modes for Kuzmin-Toomre models to 0.003 accuracy and allowing softening.

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We generalize the linear matrix method for computing normal modes in collisionless stellar disks to distribution functions with sharp edges at zero angular momentum ($L=0$). The generalization adds boundary-integral terms to the matrix equation without increasing its size. We validate the method by computing $m=2$ modes for two Kuzmin--Toomre disk models (Miyamoto $n_{\rm M}=3$ and Kalnajs $m_{\rm K}=6$ families) and comparing the eigenvalues with those obtained from an independent nonlinear matrix method based on logarithmic-spiral expansions. A systematic convergence study over grid resolution and harmonic truncation yields eigenvalues accurate to ${\sim}\,0.003$ in both pattern speed and growth rate. Unlike the nonlinear method, the linear method naturally incorporates gravitational softening, enabling the computation of eigenmodes for softened disk models. The implementation in Julia with GPU acceleration is openly available.

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astro-ph.GA 2026-07-01

LRDs average 8% solar metallicity with tight stable range

by G.P. Nikopoulos, D. Watson +5 more

The metallicities of little red dot host galaxies: LRDs are metal poor, but not pristine

The 0.6 dex spread holds from z=2 to 7 and challenges pristine-gas models for these compact high-redshift sources.

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Little Red Dots (LRDs) are a population of high-z sources discovered by JWST whose compactness, broad permitted lines, strong absorption features, continuum shapes and luminosities point to accreting supermassive black holes (SMBHs) embedded in dense gas. To date, the metallicity of the hosts of these systems has not been systematically measured. We determine the gas-phase metallicities of LRD host galaxies and test whether their narrow-line emission is consistent with metal poor star formation or AGN activity. We assemble a sample of 24 LRDs at z ~ 2.3-7 with medium and high-resolution JWST/NIRSpec data. We derive oxygen abundances and electron temperatures using the direct Te method applied exclusively to the narrow components of emission lines, and cross-check against widely used strong line calibrations. We derive a sample-averaged abundance of $Z_{T_\mathrm{e}} = 0.08_{-0.03}^{+0.11}\,\mathrm{Z_{\odot}}$ ($T_\mathrm{e} = 23000_{-7000}^{+17000}$\,K), placing LRDs firmly in the metal-poor regime of high redshift star forming galaxies. The R-hat calibration yields a consistent average of $Z_{\hat{\mathrm{R}}} = 0.07_{-0.04}^{+0.07}\,\mathrm{Z_{\odot}}$, with only 4% scatter relative to the direct Te method, providing a robust proxy for systems where the [O III]4363{\AA} line is not detected. We also identify two extremely metal-poor LRDs with metallicities <1.3%. The general population of LRDs are among the lower metallicity galaxies found by JWST at this epoch; they exhibit a narrow range of metallicities with a range of about 0.6 dex, which remains remarkably stable over cosmic time. Such low metallicity may then be a defining property of the class. The fact that LRDs have substantial metallicity across most of the class poses a challenge to models that require formation via pristine gas collapse, while their generally low metallicity indicates that they are not standard AGN.

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astro-ph.GA 2026-07-01

Review groups filament detection methods by magnetic alignment utility

by Dana Alina

Interstellar filament detection and characterization: methods and implications for studies of magnetized interstellar medium

Classification shows how different techniques affect conclusions on filament orientations relative to magnetic fields in the interstellar me

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Filamentary structures are ubiquitous in the interstellar medium and play a key role in the evolution of molecular clouds and star formation. Their morphology and relative orientation with respect to magnetic fields have been widely used as a diagnostic of magnetohydrodynamic processes, turbulence, and gravitational accretion. In recent years, the growing availability of large continuum, spectroscopic, and polarization data stimulated the development of various filament detection techniques. In this review, we present a systematic overview of filament detection methods applied to observations of the interstellar medium. We classify the existing approaches into methodological categories, discuss underlying principles, illustrate their application on a same observational field, discuss limitations and advantages, in particular with respect to the studies of the relative alignment between magnetic fields and filaments. We conclude with presenting a point of view on the perspectives for filament studies in the era of ever-growing astronomical data volume.

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astro-ph.GA 2026-07-01

Radiative losses cut high-redshift radio galaxy luminosities

by M. J. Hardcastle

A simulation-based analytic model of radio galaxies II: self-consistent radiative losses

Self-consistent inverse-Compton drain on the CMB makes sources fainter in radio and X-ray than loss-free models predict.

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The evolution of the radio properties of high-redshift radio-luminous active galactic nuclei is well known to be strongly affected by inverse-Compton losses which increase rapidly at higher redshifts due to the higher energy density in the cosmic microwave background radiation. Dynamical models of these sources, however, generally neglect the effects of radiative losses on the dynamics and energetics of the sources themselves. In the framework of an analytical model I developed in a previous paper, I show that the assumption that these losses can be neglected becomes unsafe at high redshifts. The effects on the source dynamics and energetics can result in significantly lower predicted luminosities for high-redshift sources in both radio (synchrotron) and X-ray (inverse-Compton) bands. Modelling of the population of these powerful sources needs to take account of these results in order to infer jet powers at high redshift, and also to make a correct prediction of the number of sources that may be available to provide a background for studies of the 21-cm forest.

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astro-ph.GA 2026-07-01

New instruments expand scoured galaxy core search by factor of 40

by E. Bortolas, E. Portaluri +4 more

Unveiling the properties of galaxy cores excavated by supermassive black hole binaries with SHARP

SHARP-VESPER and MICADO enable detection of black hole binary signatures up to reionization and in smaller galaxies to complement gravitatio

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Massive black hole (MBH) binaries form as a result of galaxy mergers and can coalesce into a single MBH by emitting gravitational waves detectable by LISA and pulsar timing array campaigns. Although electromagnetic observations of bound MBH binaries are extremely challenging, an indirect signature of their passage is the core scouring: a bound binary shrinks by ejecting nearby stars, creating a flat stellar density core of the size of the binary influence radius. Through this mechanism, stars on radial orbits are preferentially ejected, resulting in a central tangential anisotropy in the velocity field of stars that can be identified via IFU observations. At present, the sample of galaxies with such properties is limited by instrument resolution to the closest giant ellipticals within the nearest ~100 Mpc. The SHARP-VESPER IFU and MICADO+MORFEO instruments can work in concert to detect both these features: their unprecedented spatial resolution can allow us to detect central scourings with sizes above ~500 pc in principle up to reionization; smaller cores of ~150 pc can be detected up to z~0.14, encompassing a volume that is more than 40 times the one available at present. In addition, they can enable the search for these features in smaller galaxies, enhancing by a factor 30 the volume over which we can search for pc-size cores around 1-10 million solar mass MBHs. The fraction of scoured galaxies, combined with their kinematic and morphological properties, carry information on the amount of merging binaries, their masses and typical environment, thus knowing this will be fundamental to complement the forthcoming gravitational wave data.

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astro-ph.GA 2026-07-01

SKA to multiply known extragalactic water masers

by Andrea Tarchi, Paola Castangia +1 more

Boosting Water Maser Studies in AGN with the SKA

Unprecedented sensitivity enables statistical samples and luminosity functions at higher redshifts.

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Extragalactic water maser sources are unique tools to derive fundamental physical quantities of the host galaxies. In nearby and distant active galactic nuclei (AGN), water masers are used to determine the geometry of accretion disks around super-massive black holes, precise black hole masses, and standard-candles-independent distances to the host galaxy. In addition, they allow detailed studies of the interaction between nuclear jets/outflows and the interstellar medium, providing clues on AGN feedback mechanisms. So far, however, extragalactic maser searches have yielded detection rates of few percent, and only relatively few maser sources have been found, mostly in the nearby Universe. Because of its unprecedented sensitivity, the SKA will allow to significantly increase the number of known water maser sources especially in the more distant Universe. This will lead to the chance of performing statistically-relevant studies of the maser phenomenon (and its occurrence), derive extragalactic maser luminosity functions and, ultimately, to perform the aforementioned studies for larger samples and up to cosmological distances. In this Chapter, we will provide a quantitative analysis of the expected number of new extragalactic water maser sources already at the reach of the SKA-Mid telescope (in AA4 configuration) through targeted and blinds surveys. In addition, we will discuss the main requirements for the upcoming SKA design, in terms of baselines and frequency coverage, that may maximize the exploitation of such wealth of new targets, allowing a true step forward in AGN-related maser science.

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astro-ph.GA 2026-07-01

Neural network unifies six extinction maps into 1.9 billion stars

by Baisong Zhang, Bingqiu Chen +10 more

GSED: The Galactic Stellar Extinction Database

Query service returns corrected E(B-V), Gaia colour excess and A_V from homogenized stellar data

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Reliable extinction correction is essential for nearly all astrophysical studies within the Galaxy. We present the Galactic Stellar Extinction Database (GSED, https://nadc.china-vo.org/data/gsed/), a homogenised database that unifies six representative 3D extinction datasets under a common $E(B-V)$ and parallax-distance baseline. A six-layer multilayer perceptron is designed to correct the systematic differences in both extinction and distance across the heterogeneous input catalogues. Applying the trained models yields a catalogue of over 1.9 billion homogenised entries, which is built into a publicly accessible, real-time query service: a user supplies a coordinate and a search radius, the system retrieves the data, fits the distance--extinction relation, returns $E(B-V)$ together with $E(G_{\rm BP}-G_{\rm RP})$ and $A_V$, and allows the raw catalogue and the fitted curve to be downloaded. By delivering extinction as raw stellar measurements rather than voxelised map products and retaining the capacity to incorporate future datasets, GSED provides a flexible, traceable, and extensible new tool for Galactic extinction correction and dust-structure studies.

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