Where Do Obscured AGN Fit in A Galaxy's Timeline?

TL;DR

This study investigates the role of obscured AGNs in galaxy evolution by analyzing X-ray undetected AGNs in the COSMOS field, revealing a larger obscured AGN population and their placement on the galaxy main sequence.

Contribution

It introduces a stacking method to detect and analyze obscured AGNs in IR-selected galaxies, expanding understanding of their prevalence and properties.

Findings

X-ray undetected AGNs correlate with IR luminosity.

Obscured AGNs predominantly lie on the galaxy main sequence.

Higher obscured AGN population than previously estimated.

Abstract

Many X-ray bright active galactic nuclei (AGN) are predicted to follow an extended stage of obscured black hole growth. In support of this picture we examine the X-ray undetected AGNs in the COSMOS field and compare their host galaxies with X-ray bright AGNs. We examine galaxies with M_\ast>10^{9.5}M_\odot for the presence of AGNs at redshifts $z=0.5-3$. We select AGNs in the infrared using \textit{Spitzer} and \textit{Herschel} detections and use color selection techniques to select AGNs within strongly star forming hosts. We stack \textit{Chandra} X-ray data of galaxies with an IR detection but lacking an X-ray detection to obtain soft and hard fluxes, allowing us to measure the energetics of these AGNs. We find a clear correlation between X-ray luminosity and IR AGN luminosity in the stacked galaxies. We also find that X-ray undetected AGNs all lie on the main sequence -- the tight correlation between SFR and $M_\ast$ that holds for the majority of galaxies, regardless of mass or redshift. This work demonstrates that there is a higher population of obscured AGNs than previously thought.