HST WFC3/IR Observations of Active Galactic Nucleus Host Galaxies at z~2: Supermassive Black Holes Grow in Disk Galaxies

TL;DR

This study uses HST WFC3/IR imaging to analyze the morphologies of AGN host galaxies at redshift 1.5-3, revealing that most are disk-dominated and that black hole growth occurs mainly in these galaxies through secular processes.

Contribution

First detailed rest-frame optical morphological study of AGN hosts at z~2 showing dominance of disk galaxies in black hole growth.

Findings

80% of AGN hosts are disk-dominated

Black hole growth mainly occurs in disk galaxies

No significant morphological evolution from z~2 to z~0.05

Abstract

We present the rest-frame optical morphologies of active galactic nucleus (AGN) host galaxies at 1.5<z<3, using near-infrared imaging from the Hubble Space Telescope Wide Field Camera 3, the first such study of AGN host galaxies at these redshifts. The AGN are X-ray selected from the Chandra Deep Field South and have typical luminosities of 1E42 < L_X < 1E44 erg/s. Accreting black holes in this luminosity and redshift range account for a substantial fraction of the total space density and black hole mass growth over cosmic time; they thus represent an important mode of black hole growth in the universe. We find that the majority (~80%) of the host galaxies of these AGN have low Sersic indices indicative of disk-dominated light profiles, suggesting that secular processes govern a significant fraction of the cosmic growth of black holes. That is, many black holes in the present-day universe grew much of their mass in disk-dominated galaxies and not in early-type galaxies or major mergers. The properties of the AGN host galaxies are furthermore indistinguishable from their parent galaxy population and we find no strong evolution in either effective radii or morphological mix between z~2 and z~0.05.