X-ray Groups of Galaxies at 0.5<z<1 in zCOSMOS: Increased AGN Activities in High Redshift Groups

TL;DR

This study investigates galaxy properties at 0.5<z<1 in X-ray groups, revealing increased AGN activity and a higher fraction of red galaxies in groups compared to the field, with implications for galaxy evolution.

Contribution

It provides new insights into the environmental dependence of galaxy properties at high redshift, highlighting increased AGN activity in galaxy groups at z~1.

Findings

Higher fraction of red galaxies in groups than in the field.

Increase in red [OII] emitters at higher redshifts in groups.

Red [OII] emitters are old, with no evidence of dusty star formation.

Abstract

We present a photometric and spectroscopic study of galaxies at 0.5<z<1 as a function of environment based on data from the zCOSMOS survey. There is a fair amount of evidence that galaxy properties depend on mass of groups and clusters, in the sense that quiescent galaxies prefer more massive systems. We base our analysis on a mass-selected environment using X-ray groups of galaxies and define the group membership using a large number of spectroscopic redshifts from zCOSMOS. We show that the fraction of red galaxies is higher in groups than in the field at all redshifts probed in our study. Interestingly, the fraction of [OII] emitters on the red sequence increases at higher redshifts in groups, while the fraction does not strongly evolve in the field. This is due to increased dusty star formation activities and/or increased activities of active galactic nuclei (AGNs) in high redshift groups. We study these possibilities using the 30-band photometry and X-ray data. We find that the stellar population of the red [OII] emitters in groups is old and there is no clear hint of dusty star formation activities in those galaxies. The observed increase of red [OII] emitters in groups is likely due to increased AGN activities. However, our overall statistics is poor and any firm conclusions need to be drawn from a larger statistical sample of z~1 groups.