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

TL;DR

This study investigates the properties of host galaxies of X-ray detected AGN in the local universe, revealing differences in stellar mass and star formation activity between type 1 and type 2 AGN, and providing insights into their evolutionary states.

Contribution

It provides a detailed analysis of host galaxy properties of X-ray AGN using multi-wavelength data and compares type 1 and type 2 AGN in the local universe, highlighting differences in stellar mass and star formation.

Findings

Type 2 AGN reside in more massive galaxies than type 1.

Most AGN are found in or above the main sequence of star formation.

In the local universe, more AGN are in quiescent systems compared to higher redshifts.

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.