MusE GAs FLOw and Wind (MEGAFLOW) X. The cool gas and covering fraction of MgII in galaxy groups

TL;DR

This study investigates the distribution and properties of cool MgII gas around galaxy groups, revealing that MgII halos extend further and are more prevalent in groups than in isolated galaxies, with profiles resembling dark matter halos.

Contribution

It provides the first detailed analysis of MgII absorption in galaxy groups at intermediate redshifts, showing how MgII halos scale with group mass and compare to dark matter profiles.

Findings

MgII absorption systems are associated with 21 out of 120 systems in the survey.

MgII halos extend to about one virial radius, with covering fractions exceeding 50%.

The cool gas column density profile closely follows dark matter halo profiles.

Abstract

We present a study of the cool gas ($\approx 10^4$ K) traced by MgII absorptions around groups of galaxies in the MEGAFLOW survey. Using a combination of two algorithms we blindly identify 32 groups of more than 5 galaxies at $0.3 < z < 1.5$ with $10.7 < \log_{10}(M/\rm M_{\odot}) < 13.7$. Among them 26 can be used to study potential counterpart MgII absorptions. We report that 21 out of the total 120 MgII absorption systems present in MEGAFLOW are associated with groups. We observe that the MgII rest-frame equivalent width ($W^{2796}_r$) drops at an impact parameter of $\approx 150$ projected kpc from the closest galaxy and $\approx$ one virial radius from the identified group center indicating that MgII halos scale with the mass of the groups.The impact parameter where the covering fraction exceeds $50\%$ is $\log_{10}(b/\rm kpc) = 2.17 \pm 0.47$ $(2 \sigma)$ and $(b/R_{\rm vir}) = 1.67 \pm 0.98$, which is $\approx 3$ times larger than for field galaxies ($\log_{10}(b/\rm kpc)=1.67\pm0.15$). Finally, we estimate the cool gas column density profile in groups (from the $W^{2796}_r$) and show that its shape follows closely the typical dark matter column density profile for halos at similar redshift and masses.