This paper delivers the first population-level look at MgII-emitting halos around 47 star-forming galaxies at 0.7
Referee Report
2 major / 2 minor
Summary. The manuscript presents the first statistical study of extended Mg II emission tracing galactic outflows in 47 star-forming galaxies at 0.7 < z < 2.0 observed with MUSE. Extending a prior single-object modeling framework, the authors model the halos as ensembles of radially accelerating shells and report consistency with linear acceleration from launch velocities of ~60 km/s to maximum velocities reaching ~490 km/s that correlate with stellar mass. They identify associated trends with SFR, sSFR, stellar population age, central optical depth, outflow opening angle, and halo half-light radii (peaking at ~5 kpc with a tail to ~20 kpc), including a distinction between compact and extended halos.
Significance. If the modeling framework and its assumptions are validated, the work supplies the first population-level constraints on outflow kinematics and geometry from Mg II emission, moving the field beyond individual case studies toward statistical trends that can be compared with simulations of star-formation-driven winds. The sample size and forward-modeling approach are clear strengths.
major comments (2)
- [§3] §3 (outflow modeling framework): the central claim that the data are consistent with radially accelerating shells whose velocity increases linearly with radius rests on extending the single-object shell geometry without reported comparisons to alternative profiles (constant-velocity, decelerating, or non-shell geometries). This assumption directly determines the reported launch velocity (~60 km/s), maximum velocity (~490 km/s), and linear radial dependence; if other profiles fit equally well, these specific quantitative statements do not follow uniquely from the observations.
- [Results] Results section (velocity and correlation trends): the reported maximum velocities, stellar-mass correlations, and compact vs. extended halo distinctions lack visible error bars, uncertainty quantification, or robustness checks against sample selection and post-hoc HLR cuts (HLR < 8 kpc). This undermines assessment of whether the trends are statistically significant or sensitive to modeling choices.
minor comments (2)
- [Abstract] Abstract and §4: the post-hoc separation into compact and extended halos would benefit from a pre-specified size threshold or sensitivity test to confirm it does not drive the reported differences in powering mechanisms.
- [Sample] Sample description: additional details on selection criteria, completeness, and any biases in the 47-galaxy sample would clarify the generality of the population trends.
Simulated Author's Rebuttal
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unresolved
We thank the referee for their constructive review and positive assessment of the work's significance. We address each major comment point by point below, providing the strongest honest defense of the manuscript while acknowledging where revisions are warranted.
read point-by-point responses
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Authors: The modeling framework was developed and validated through detailed fitting in our prior single-object study, where the linear radial acceleration provided the best match to the observed Mg II kinematics and surface brightness profiles. For the current statistical sample of 47 galaxies, we extended this same framework to derive population-level constraints. While we agree that explicit comparisons to constant-velocity or decelerating profiles are not presented here, such alternatives were not favored in the original validation and would require substantial additional computational resources for the full sample. In revision, we will add a dedicated paragraph in §3 discussing the physical motivation (e.g., consistency with radiation-pressure-driven wind models) and note the limitations of not testing alternatives in this work.
revision: partial
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Authors: We agree that the results section would be strengthened by explicit uncertainty quantification. The reported velocities and correlations are derived from the forward-modeling posteriors, but these were not visualized with error bars in the submitted version. In the revised manuscript, we will add error bars to all velocity and correlation plots, report the median uncertainties from the modeling, and include a new subsection with robustness tests against sample selection effects and the HLR < 8 kpc cut (e.g., repeating the trends with varied thresholds and reporting p-values or Spearman coefficients with uncertainties). This will allow readers to assess the statistical significance directly.
revision: yes
Circularity Check
0 steps flagged
No significant circularity in derivation chain
full rationale
The paper applies a forward-modeling framework (ensemble of radially accelerating shells) developed in prior single-object work to new MUSE data on 47 galaxies at 0.7<z<2.0. Reported quantities such as launching velocities (~60 km/s), maximum velocities (~490 km/s), linear radial acceleration, optical depths, and opening angles are direct outputs of fitting this model to the observed Mg II surface-brightness and kinematics profiles. No step renames a fitted parameter as an independent prediction, invokes a self-citation uniqueness theorem, or reduces the central statistical claims to the inputs by construction. The self-citation serves only to reference the method; the population-level constraints remain data-driven and falsifiable against the current sample. The derivation is therefore self-contained.
Axiom & Free-Parameter Ledger
4 free parameters ·
2 axioms ·
0 invented entities
Central claims rest on the domain assumption that extended MgII traces star-formation-driven outflows modeled as radially accelerating shells, with several fitted parameters for velocity, opacity, and geometry derived from the MUSE data.
free parameters (4)
- launching velocity =
~60 km/s
Starting speed of the accelerating shells fitted to match observed emission profiles.
- maximum velocity =
~490 km/s
Terminal speed of the wind, reported to correlate with stellar mass.
- central optical depth
Opacity parameter showing tentative stellar-mass trend.
- opening angle
Angular width of the outflow cone, varying with stellar mass.
axioms (2)
- domain assumption MgII emission traces galactic-scale outflows driven by star formation
Standard assumption in the field, invoked to interpret the extended halos as wind signatures.
- domain assumption Outflows can be modeled as an ensemble of radially accelerating shells
Carried forward from the authors' prior single-object framework and applied to the statistical sample.
pith-pipeline@v0.9.0 ·
5705 in / 1527 out tokens ·
204869 ms ·
2026-05-16T02:05:54.008748+00:00
· methodology
read the original abstract
Galaxies evolve within vast gaseous halos that fuel star formation and carry signatures of feedback-driven outflows. Deep integral field data have enabled the study of MgII halos, which trace galaxy-scale outflows in emission, but their faintness has limited studies to single-object analyses. Here, we present the first statistical study of MgII-emitting halos using deep MUSE observations of 47 star-forming galaxies at $0.7<z<2.0$. Building on our previous work, where we developed and applied an outflow modeling framework for a single MgII halo, we now extend this approach to a larger sample, enabling robust population-level insights on the properties of circumgalactic outflows traced by their extended MgII emission. We detect extended emission out to tens of kiloparsecs and model the outflows as an ensemble of radially accelerating shells. Galaxies with MgII outflows tend to have higher SFRs, sSFRs, and younger stellar populations, consistent with star-formation-driven winds. The observations are consistent with winds that accelerate linearly with radius, from launching velocities of ~60 km/s up to maximum velocities that correlate with stellar mass and reach ~490 km/s. Their inner regions are highly opaque, and we find a tentative trend between stellar mass and central optical depth. The opening angle of the outflow shows some dependency on the host-galaxy stellar mass, with less massive galaxies showing primarily wide opening angles, and more massive galaxies showing a broader range of values, with both wide and narrow opening angles. The distribution of the spatial extent of MgII halos exhibits a clear peak at half-light radius (HLR) of ~5 kpc, with an extended tail of larger HLR values, up to ~20 kpc. Compact halo sizes (HLR $< 8$ kpc) correlate with stellar mass, but extended halos do not, which could suggest a difference in the powering mechanism between compact and extended halos.