On the occupation of X-ray selected galaxy groups by radio AGN since z=1.3

Previous clustering analysis of low-power radio AGN has indicated that they preferentially live in massive groups. The X-ray surveys of the COSMOS field have achieved a sensitivity at which these groups are directly detected out to z=1.3. Making use of Chandra-, XMM- and VLA-COSMOS surveys we identify radio AGN members (1023.6 < L_1.4GHz/(W/Hz) < 1025) of galaxy groups (1013.2 < M_200/M_sun < 1014.4; 0.1<z<1.3) and study i) the radio AGN – X-ray group occupation statistics as a function of group mass, and ii) the distribution of radio AGN within the groups. We find that radio AGN are preferentially associated with galaxies close to the center (< 0.2r_200). Compared to our control sample of group members matched in stellar mass and color to the radio AGN host galaxies, we find a significant enhancement of radio AGN activity associated with 1013.6 < M_200/M_sun < 1014 halos. We present the first direct measurement of the halo occupation distribution (HOD) for radio AGN, based on the total mass function of galaxy groups hosting radio AGN. Our results suggest a possible deviation from the usually assumed power law HOD model. We also find an overall increase of the fraction of radio AGN in galaxy groups (<1r_200), relative to that in all environments.