Host galaxy properties of X-ray AGN in the Local Universe

Abstract

We study the host galaxy properties of active galactic nuclei (AGN) that have been detected in X-rays in the nearby Universe ($\rm z<0.2$). For that purpose, we use the catalogue provided by the ROSAT-2RXS in the 0.1-2.4\,keV energy band, one of the largest X-ray datasets with spectroscopic observations. Our sample consists of $\sim 900$ X-ray AGN. The catalogue provides classification of the sources into type 1 and 2, based on optical spectra. $\sim 25\%$ of the AGN are type 2. We use the available optical, near-IR and mid-IR photometry to construct SEDs. We measure the stellar mass ($M_*$) and star formation rate (SFR) of the AGN, by fitting these SEDs with the X-CIGALE code. We compare the $M_*$ and SFR of the two AGN populations, taking into account their different redshift and luminosity distributions. Based on our results, type 2 AGN tend to live in more massive galaxies compared to their type 1 counterparts ($\rm log\,[M_*(M_\odot)]=10.49^{+0.16}_{-0.10}$ vs. $10.23^{+0.05}_{-0.08}$), in agreement with previous studies at higher redshifts. In terms of SFR, our analysis shows, that in the nearby Universe, the number of X-ray AGN that live in quiescent systems is increased compared to that at higher redshifts, in accordance with previous studies in the local universe. However, the majority of AGN ($\sim 75\%$) live inside or above the main sequence.