SIMBAD references

We describe X-ray observations with Chandra and XMM-Newton of 18 M_group∼ 1-6x10¹³ M_☉, z ∼ 0.05 galaxy groups from the Zurich ENvironmental Study. The X-ray data aim at establishing the frequency and properties, unaffected by host galaxy dilution and obscuration, of active galactic nuclei (AGNs) in central and satellite galaxies, also as a function of halo-centric distance. X-ray point-source detections are reported for 22 of the 177 galaxies, down to a sensitivity level of f_0.5 - 8 keV_∼ 5x10^–15 erg/cm2/s, corresponding to a limiting luminosity of L_0.5 - 8 keV_∼ 3x10⁴⁰ erg/s. With the majority of the X-ray sources attributed to AGNs of low-to-moderate levels (L/L_Edd ≳ 10^–4), we discuss the detection rate in the context of the occupation of AGNs to halos of this mass scale and redshift and compare the structural and morphological properties between AGN-active and non-active galaxies. At galaxy mass scales <10¹¹ M_☉, central galaxies appear to be a factor of ∼4 more likely to host AGNs than satellite galaxies of similar mass. This effect, coupled with the tendency for AGNs to be hosted by massive galaxies, explains the (weak) trend for AGNs to be preferentially found in the inner parts of group halos, with no detectable trend with halo-centric distance in the frequency of AGNs within the satellite population. Finally, our data indicate that the rate of decline with redshift of AGN activity in galaxy groups matches that of the global AGN population, indicating that either AGN activity occurs preferentially in group halos or that the evolution rate is independent of halo mass.