The relation between AGN type and host galaxy properties

TL;DR

This study analyzes a large sample of AGNs to investigate the relationship between AGN type, host galaxy properties, and AGN power, finding no significant link between AGN obscuration and host galaxy star formation or mass.

Contribution

It provides a comprehensive analysis of the connection between AGN obscuration, host galaxy properties, and AGN luminosity using Bayesian methods and a large dataset, supporting the standard AGN unification model.

Findings

No significant link between AGN type and host galaxy star formation or mass.

The correlation between X-ray luminosity and normalized SFR is consistent across AGN types.

Obscuration level (N_H) is not related to the host galaxy's star formation rate.

Abstract

We use 3,213 Active Galactic Nuclei (AGNs) from the $\it{XMM}$-XXL northern field to investigate the relation of AGN type with host galaxy properties. Applying a Bayesian method, we derive the hardness ratios (HRs) and through these the hydrogen column density ($\rm N_H$) for each source. We consider as absorbed sources (type-2) those with $\rm N_H > 10^{21.5}\, \rm{cm^{-2}}$. We examine the star formation rate (SFR) as well the stellar mass (M$_*$) distributions for both absorbed and unabsorbed sources. Our work indicates that there is no significant link between the AGN type and these host galaxy properties. Next, we investigate whether the AGN power, as represented by its X-ray luminosity, $\rm L_X$, correlates with any deviation of the host galaxy's place from the so-called Main Sequence of galaxies, and we examine this separately for the obscured and the unobscured AGN populations. To take into account the effect of M$_*$ and redshift on SFR, we use the normalised SFR (SFR$_{norm}$). We find that the correlation between $\rm L_X$ and SFR$_{norm}$, follows approximately the same trend for both absorbed and unabsorbed sources, a result that favours the standard AGN unification models. Finally, we explore the connection between the obscuration, $\rm N_H$, and the SFR. We find that there is no relation between these, suggesting that the obscuration is not related to the large scale SFR in the galaxy.