The link among X-ray spectral properties, AGN structure, and the host galaxy

Abstract

In this work, we compare the supermassive black hole (SMBH) and host galaxy properties of X-ray obscured and unobscured AGN. For that purpose, we used $ 35\,000$ X-ray detected AGN in the 4XMM-DR11 catalogue for which there are available measurements for their X-ray spectral parameters, such as the hydrogen column density, N$_H$, and photon index, Gamma , from the XMM2Athena Horizon 2020 European project. We constructed the spectral energy distributions (SEDs) of the sources, and we calculated the host galaxy properties via SED fitting analysis, utilising the CIGALE code. We applied strict photometric requirements and quality selection criteria to include only sources with robust X-ray and SED fitting measurements. Our sample consists of 1\,443 AGN. In the first part of our analysis, we used different N$_H$ thresholds $) while also taking into account the uncertainties associated with the N$_H$ measurements in order to classify these sources as obscured and unobscured (or mildly obscured). We find that obscured AGN tend to live in more massive systems (by $ 0.1$\,dex) that have a lower star-formation rate, SFR, (by $ 0.25$\,dex) compared to their unobscured counterparts. However, only the difference in stellar mass, M$_*$, appears statistically significant ($>2 The results do not depend on the N$_H$ threshold used to classify AGN. The differences in M$_*$ and SFR are not statistically significant for luminous AGN ($ X,2-10\,KeV )> 44$). Our findings also show that unobscured AGN have, on average, higher specific black hole accretion rates, $ sBHAR $, compared to their obscured counterparts, a parameter which is often used as a proxy of the Eddington ratio. In the second part of our analysis, we cross-matched the 1\,443 X-ray AGN with the SDSS DR16 quasar catalogue of Wu and Shen to obtain information on the SMBH properties of our sources. This resulted in 271 type 1 AGN at $ z<1.9$. Our findings show that type 1 AGN with increased N$_H$ $) tend to have higher black hole masses, M$_ BH $, compared to AGN with lower N$_H$ values at similar M$_*$. The M$_ BH $, but it exhibits signs of increasing at higher N$_H$ values. Finally, we detected a correlation between Gamma and Eddington ratios, but only for type 1 sources with N$_H<10^

The properties of supermassive black holes and their host galaxies for type 1 and 2 active galactic nuclei in the eFEDS and COSMOS fields

“…Georgantopoulos et al attribute the disparities observed in their results, in contrast to prior research that found no discernible distinctions in the properties of host galaxies between X-ray absorbed and unabsorbed AGNs (e.g., Masoura et al 2021;Mountrichas et al 2021c), or research employing optical criteria (e.g., Zou et al 2019;Mountrichas et al 2021a) by different sample sets. Mountrichas et al (2024) used Xray AGNs from the 4XMM dataset and applied strict X-ray criteria for the AGN classification (N H = 10 23 cm −2 ), taking into account also the uncertainties associated with the N H measurements. Their findings closely mirror those reported in the study by Georgantopoulos et al (2023) concerning the host galaxy properties of the two AGN populations.…”

“…They attribute these divergent findings compared to previous investigations to either the elevated N H threshold employed or the varying X-ray luminosities probed by the datasets used across different studies. Mountrichas et al (2024) have built upon these insights by employing X-ray AGN data from the 4XMM catalog and implementing rigorous X-ray criteria for AGN classification. Their results closely mirror those obtained by Georgantopoulos et al (2023), reinforcing the observed differences in host galaxy properties between X-ray obscured and unobscured AGNs.…”