Galaxy Clusters in the Line of Sight to Background Quasars: II. Environmental effects on the sizes of baryonic halo sizes

TL;DR

This study investigates how galaxy cluster environments influence the sizes of baryonic halos around galaxies, using empirical and semi-analytic models to match observed MgII absorption statistics.

Contribution

It provides the first combined analysis of MgII halo sizes in cluster versus field environments using two independent models, revealing significant halo size reduction in clusters.

Findings

Field MgII halo size ~50h_71^-1kpc consistent with previous studies.

Cluster MgII halo size <10h_71^-1kpc needed to match observations.

Stronger absorption systems are located closer to the halo center, with weaker systems occurring at smaller fractions of the halo size near cluster centers.

Abstract

Based on recent results on the frequency of MgII absorption line systems in the "QSO behind RCS clusters" survey (QbC), we analyse the effects of the cluster environment on the sizes of baryonic haloes around galaxies. We use two independent models, i) an empirical halo occupation model which fits current measurements of the clustering and luminosity function of galaxies at low and high redshifts, and ii) the GALFORM semi-analytic model of galaxy formation, which follows the evolution of the galaxy population from first principles, adjusted to match the statistics of low and high redshift galaxies. In both models we constrain the MgII halo sizes of field and cluster galaxies using observational results on the observed MgII statistics. Our results for the field are in good agreement with previous works, indicating a typical \mgii\ halo size of $r_MgII ~ 50h_71^-1kpc in the semi-analytic model, and slightly lower in the halo occupation number approach. For the cluster environment, we find that both models require a median MgII halo size of r_MgII< 10h_71^-1kpc in order to reproduce the observed statistics on absorption line systems in clusters of galaxies. Based on the Chen & Tinker (2008) result that stronger systems occur closer to the MgII halo centre, we find that strong absorption systems in clusters of galaxies occur at roughly a fixed fraction of the cold-warm halo size out to 1h_71^-1Mpc from the cluster centres. In contrast, weaker absorption systems appear to occur at progressively shorter relative fractions of this halo as the distance to the cluster centre decreases.