Relation between AGN type and host galaxy properties

¹ National Observatory of Athens, V. Paulou & I. Metaxa, 15 236 Penteli, Greece
e-mail: vassi.lia.mas@gmail.com
² Section of Astrophysics, Astronomy and Mechanics, Department of Physics, Aristotle University of Thessaloniki, 54 124 Thessaloniki, Greece
³ Instituto de Fisica de Cantabria (CSIC-Universidad de Cantabria), Avenida de los Castros, 39005 Santander, Spain

Received: 22 August 2020
Accepted: 3 January 2021

Abstract

We use 3213 active galactic nuclei (AGNs) from the XMM-XXL northern field to investigate the relation of AGN type with host galaxy properties. Applying a Bayesian method, we derive the hardness ratios, and through these the hydrogen column density (N_H) for each source. We consider those with N_H > 10^21.5 cm⁻² as absorbed sources (type 2). We examine the star formation rate (SFR) and the stellar mass (M_*) distributions for both absorbed and unabsorbed sources. Our work indicates that there is no significant link between AGN type and these host galaxy properties. Next, we investigate whether the AGN power, as represented by its X-ray luminosity (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 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 (N_H) and the SFR. We find that there is no relation between them, suggesting that obscuration is not related to the large-scale SFR in the galaxy.