Building the first sample of mgii absorbers in clusters/groups of galaxies

Abstract

This study presents Gemini/GMOS-S multi-object spectroscopy of 31 highredshift galaxy cluster candidates, lying at a projected distance < 2 h:¡l M pe from 9 quasar sight-lines, where Mg II absorption systems have been previously detected ata redshift similar to that of the galaxy cluster candidates (program ID: GS-2008A-Q-10; PI: S. López). This sample has been taken from López et al. (2008). The absorption systems span rest-frame equivalent widths 0.015 ::::; W5796 ::::; 2.028 Á, and absorption redshifts 0.2507 ::::; Zabs ::::; 1.0951. The aim of this work is three-fold: 1) find the absorbing galaxies, 2) confirm spectroscopically the presence of galaxy clusters in the vicinity of each quasar sight-line, and 3) confirm whether the galaxies hosting the absorbers reside in galaxy clusters or not. The main result is that out of 23 absorption systems, 8 Mg II absorbers are found in galaxy clusters of M200 rv 2 X 1014 M0, and 4 in galaxy groups. The absorbing galaxies have luminosities L8 rv L'B and mean restframe colors (Re - z') typical of Sbc-Scd galaxies. Those residing in clusters of galaxies host weak absorbers and appear to be consistent with a lower star formation activity than the absorbing galaxies found in the field. These last ones produce strong absorptions and appear as typical isolated absorbing galaxies found in the literature. Also the number density and equivalent width distribution of weak Mg II absorbers in clusters of galaxies agree with the field expectations as stated in López et al. (2008), even when constraining further the redshift path of the survey according to our confirmations of clusters of galaxies.