The evolution of the AGN content in groups up to z~1. (arXiv:1302.2861v1 [astro-ph.CO])

The evolution of the AGN content in groups up to z~1. (arXiv:1302.2861v1 [astro-ph.CO]):
Determining the AGN content in structures of different mass/velocity
dispersion and comparing them to higher mass/lower redshift analogs is
important to understand how the AGN formation process is related to
environmental properties. We use our well-tested cluster finding algorithm to
identify structures in the GOODS North and South fields, exploiting the
available spectroscopic redshifts and accurate photometric redshifts. We
identify 9 structures in GOODS-south (presented in a previous paper) and 8 new
structures in GOODS-north. We only consider structures where at least 2/3 of
the members brighter than M_R=-20 have a spectroscopic redshift. For those
group members that coincide with X-ray sources in the 4 and 2 Msec Chandra
source catalogs respectively, we determine if the X-ray emission originates
from AGN activity or it is related to the galaxies' star-formation activity. We
find that the fraction of AGN with Log L_H > 42 erg/s in galaxies with M_R <
-20 is on average 6.3+-1.3%, much higher than in lower redshift groups of
similar mass and more than double the fraction found in massive clusters at a
similarly high redshift. We then explore the spatial distribution of AGN in the
structures and find that they preferentially populate the outer regions. The
colors of AGN host galaxies in structures tend to be confined to the green
valley, thus avoiding the blue cloud and, partially, also the red-sequence,
contrary to what happens in the field. We finally compare our results to the
predictions of two sets of semi analytic models to investigate the evolution of
AGN and evaluate potential triggering and fueling mechanisms. The outcome of
this comparison attests the importance of galaxy encounters, not necessarily
leading to mergers, as an efficient AGN triggering mechanism. (abridged)