The role of AGN and its obscuration on the position of the host galaxy relative to Main Sequence

TL;DR

This study investigates how active galactic nuclei (AGN) and their obscuration influence the star formation activity of host galaxies relative to the main sequence, using X-ray observations and spectral energy distribution fitting.

Contribution

It provides a uniform analysis of the SFR-LX relation across different galaxy masses and redshifts, highlighting the role of AGN in star formation enhancement in less massive galaxies.

Findings

AGN enhances SFR by ~50% in less massive galaxies.

No evolution of SFR normalization with redshift.

X-ray absorption not linked to host galaxy properties.

Abstract

We use X-ray Active Galactic Nuclei (AGN) observed by the Chandra X-ray Observatory within the 9.3 deg$^2$ Bo$\rm \ddot{o}$tes field of the NDWFS to study whether there is a correlation between X-ray luminosity (L$_X$) and star formation rate (SFR) of the host galaxy, at $\rm 0.5<z<2.0$, with respect to the position of the galaxy to the main sequence (SFR$_{norm}$). About half of the sources in the X-ray sample have spectroscopic redshifts. We also construct a reference galaxy catalogue. For both datasets, we use photometric data from optical to the far infrared, compiled by the HELP project and apply spectral energy distribution (SED) fitting, using the X-CIGALE code. We exclude quiescent sources from both the X-ray and the reference samples. We also account for the mass completeness of our dataset, in different redshifts bins. Our analysis highlights the importance of studying the SFR-L$_X$ relation, in a uniform manner, taking into account the systematics and selection effects. Our results suggest that, in less massive galaxies ($\rm log\,[M_*(M_\odot)] \sim 11$), AGN enhances the SFR of the host galaxy by $\sim 50\%$ compared to non AGN systems. A flat relation is observed for the most massive galaxies. SFR$_{norm}$ does not evolve with redshift. The results, although tentative, are consistent with a scenario in which, in less massive systems, both AGN and star formation (SF) are fed by cold gas, supplied by a merger event. In more massive galaxies, the flat relation could be explained by a different SMBH fuelling mechanism that is decoupled from the star formation of the host galaxy (e.g. hot diffuse gas). Finally, we compare the host galaxy properties of X-ray absorbed and unabsorbed sources. Our results show no difference which suggests that X-ray absorption is not linked with the properties of the galaxy.