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Spectroscopic Quantification of Projection Effects in the SDSS redMaPPer Galaxy Cluster Catalogue

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arxiv 2011.07070 v2 pith:3YGRMR2S submitted 2020-11-13 astro-ph.CO

Spectroscopic Quantification of Projection Effects in the SDSS redMaPPer Galaxy Cluster Catalogue

classification astro-ph.CO
keywords clusterprojectioneffectsrichnessgalaxyredmappersdssspectroscopic
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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Projection effects, whereby galaxies along the line-of-sight to a galaxy cluster are mistakenly associated with the cluster halo, present a significant challenge for optical cluster cosmology. We use statistically representative spectral coverage of luminous galaxies to investigate how projection effects impact the low-redshift limit of the Sloan Digital Sky Survey (SDSS) redMaPPer galaxy cluster catalogue. Spectroscopic redshifts enable us to differentiate true cluster members from false positives and determine the fraction of candidate cluster members viewed in projection. Our main results can be summarized as follows: first, we show that a simple double-Gaussian model can be used to describe the distribution of line-of-sight velocities in the redMaPPer sample; second, the incidence of projection effects is substantial, accounting for $\sim 16$ per cent of the weighted richness for the lowest richness objects; third, projection effects are a strong function of richness, with the contribution in the highest richness bin being several times smaller than for low-richness objects; fourth, our measurement has a similar amplitude to state-of-the-art models, but finds a steeper dependence of projection effects on richness than these models; and fifth, the slope of the observed velocity dispersion--richness relation, corrected for projection effects, implies an approximately linear relationship between the true, three-dimensional halo mass and three-dimensional richness. Our results provide a robust, empirical description of the impact of projection effects on the SDSS redMaPPer cluster sample and exemplify the synergies between optical imaging and spectroscopic data for studies of galaxy cluster astrophysics and cosmology.

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Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Impact of projection-induced optical selection bias on the weak lensing mass calibration of galaxy clusters

    astro-ph.CO 2025-10 unverdicted novelty 6.0

    Projection-induced selection bias causes 20-50% overestimation of weak lensing masses for optically selected galaxy clusters, larger on scales >3 Mpc.