X-ray selected AGN Hosts are Similar to Inactive Galaxies out to z=3: Results from CANDELS/CDF-S

TL;DR

This study compares the properties of X-ray selected AGN host galaxies to inactive galaxies up to redshift 3, finding remarkable similarities in their stellar populations and colors, which informs galaxy evolution models.

Contribution

It provides the first detailed analysis of resolved host galaxy properties of AGNs at z~2, accounting for nuclear contamination and stellar mass effects.

Findings

AGN hosts have similar stellar populations to inactive galaxies of the same mass.

At z~1, AGN hosts show slightly narrower color ranges and signs of recent star formation.

Differences between AGN hosts and inactive galaxies diminish at z~2.

Abstract

We use multi-band spatially resolved photometry from the Cosmic Assembly Near-IR Deep Legacy Survey (CANDELS) in the 4 MSec Chandra Deep Field-South (CDF-S) to explore the nuclear and extended colors, color gradients and stellar populations of X-ray selected AGN host galaxies out to z=3. Based on a study of their central light, we develop X-ray based criteria to exclude objects with strong AGN contamination. We use stellar masses from the FIREWORKS database to understand and account for stellar mass selection effects, and carefully study, for the first time, the resolved host galaxy properties of AGNs at z~2 in their rest-frame optical light without substantial nuclear contamination. AGN hosts span a sizable range of stellar masses, colors and color gradients at these redshifts. Their colors, color gradients and stellar population properties are very similar to inactive galaxies of the same stellar mass. At z~1, we find a slightly narrower range in host colors compared to inactive galaxies, as well as hints of more recent star-formation. These differences are weaker or non-existent among AGN hosts at z~2. We discuss the importance of AGN driven feedback in the quenching of galaxies at z>~1 and speculate on possible evolution in the relationship between black hole accretion and the host galaxy towards high redshifts.