X-ray selected AGN in groups at redshifts z~1

TL;DR

This study investigates how the environment of galaxy groups at redshifts 0.7 to 1.4 influences the occurrence and properties of X-ray selected active galactic nuclei (AGN), revealing their distribution and luminosity trends across different environments.

Contribution

It provides the first detailed analysis of the relationship between galaxy group environments and AGN activity at z~1, highlighting environmental effects on AGN fraction and luminosity.

Findings

X-ray AGN are more frequently found in groups than in the general galaxy population.

The AGN fraction in groups at z~1 is similar to that in low-redshift clusters and the field.

Field AGN tend to be more X-ray luminous than those in groups.

Abstract

We explore the role of the group environment in the evolution of AGN at the redshift interval 0.7<z<1.4, by combining deep Chandra observations with extensive optical spectroscopy from the All-wavelength Extended Groth strip International Survey (AEGIS). The sample consists of 3902 optical sources and 71 X-ray AGN. Compared to the overall optically selected galaxy population, X-ray AGN are more frequently found in groups at the 99% confidence level. This is partly because AGN are hosted by red luminous galaxies, which are known to reside, on average, in dense environments. Relative to these sources, the excess of X-ray AGN in groups is significant at the 91% level only. Restricting the sample to 0.7<z<0.9 and M_B<-20mag in order to control systematics we find that X-ray AGN represent (4.7\pm1.6) and (4.5\pm1.0)% of the optical galaxy population in groups and in the field respectively. These numbers are consistent with the AGN fraction in low redshift clusters, groups and the field. The results above, although affected by small number statistics, suggest that X-ray AGN are spread over a range of environments, from groups to the field, once the properties of their hosts (e.g. colour, luminosity) are accounted for. There is also tentative evidence, significant at the 98% level, that the field produces more X-ray luminous AGN compared to groups, extending similar results at low redshift to z~1. This trend may be because of either cold gas availability or the nature of the interactions occurring in the denser group environment (i.e. prolonged tidal encounters).