The Spitzer-IRAC/MIPS Extragalactic Survey (SIMES): II enhanced nuclear accretion rate in galaxy groups at z$\sim$0.2

Abstract

For a sample of star forming galaxies in the redshift interval 0.15$<$z$<$0.3, we study how both the relative strength of the AGN infra-red emission, compared to that due to the star formation (SF), and the numerical fraction of AGNs, change as a function of the total stellar mass of the hosting galaxy group (M${}_{\mathrm{group}}^{\ast }$), between $10^{10.25}$ and $10^{11.9}$M${}_{\odot }$. Using a multi-component SED fitting analysis, we separate the contribution of stars, AGN torus and star formation to the total emission at different wavelengths. This technique is applied to a new multi-wavelength data-set in the SIMES field (23 not redundant photometric bands), spanning the wavelength range from the UV (GALEX) to the far-IR (Herschel) and including crucial AKARI and WISE mid-IR observations (4.5 μm$<\hat{I}»<$24 μm), where the BH thermal emission is stronger. This new photometric catalog, that includes our best photo-z estimates, is released through the NASA/IPAC Infrared Science Archive (IRSA). Groups are identified through a friends of friends algorithm ($\sim$62% purity, $\sim$51% completeness). We identified a total of 45 galaxies requiring an AGN emission component, 35 of which in groups and 10 in the field. We find BHAR$\propto ($M${}_{\mathrm{group}}^{\ast }{)}^{1.21\pm 0.27}$ and (BHAR/SFR)$\propto ($M${}_{\mathrm{group}}^{\ast }{)}^{1.04\pm 0.24}$ while, in the same range of M${}_{\mathrm{group}}^{\ast }$, we do not observe any sensible change in the numerical fraction of AGNs. Our results indicate that the nuclear activity (i.e. the BHAR and the BHAR/SFR ratio) is enhanced when galaxies are located in more massive and richer groups.

31 pages, 23 figures