Moderate-Luminosity Growing Black Holes From 1.25 < z < 2.7: Varied Accretion In Disk-Dominated Hosts

TL;DR

This study analyzes the properties of moderate-luminosity AGN at redshifts 1.25 to 2.7, revealing diverse host galaxy morphologies and accretion rates, with implications for galaxy-black hole co-evolution.

Contribution

It provides detailed measurements of black hole growth and host galaxy characteristics at high redshift, highlighting the dominance of secular processes over major mergers.

Findings

Most AGN have low Eddington ratios (<0.1).

Over half of host galaxies are disk-dominated.

Less than 15% show signs of major mergers.

Abstract

We compute black hole masses and bolometric luminosities for 57 active galactic nuclei (AGN) in the redshift range 1.25 < z < 2.67, selected from the GOODS-South deep multi-wavelength survey field via their X-ray emission. We determine host galaxy morphological parameters by separating the galaxies from their central point sources in deep HST images, and host stellar masses and colors by multi-wavelength SED fitting. 90% of GOODS AGN at these redshifts have detected rest-frame optical nuclear point sources; bolometric luminosities range from 2e43 - 2e46 erg/s. The black holes are growing at a range of accretion rates, with at least 50% of the sample having L/L_Edd < 0.1. 70% of host galaxies have stellar masses M* > 1e10 M_sun, with a range of colors suggesting a complex star formation history. We find no evolution of AGN bolometric luminosity within the sample, and no correlation between AGN bolometric luminosity and host stellar mass, color or morphology. Fully half the sample of host galaxies is disk-dominated, with another 25% having strong disk components. Fewer than 15% of the systems appear to be at some stage of a major merger. These moderate-luminosity AGN hosts are therefore inconsistent with a dynamical history dominated by mergers strong enough to destroy disks, indicating minor mergers or secular processes dominate the co-evolution of galaxies and their central black holes at z ~ 2.