BH Accretion in Low-Mass Galaxies Since z~1

TL;DR

This study investigates black hole growth in low-mass galaxies since redshift 1, revealing strong evolution and a high prevalence of active galactic nuclei, with implications for black hole occupation fractions.

Contribution

It provides the first comprehensive analysis of AGN activity and black hole accretion in low-mass galaxies over cosmic time, highlighting their significant role in galaxy evolution.

Findings

AGN fraction increases with host mass

Strong cosmic evolution in low-mass AGNs

Estimated >50% of low-mass galaxies host black holes

Abstract

We have selected a sample of X-ray emitting active galactic nuclei (AGNs) in low-mass host galaxies (5e9-2e10 Msun) out to z~1. By comparing to AGNs in more massive hosts, we have found that the AGN spatial number density and the fraction of galaxies hosting AGNs depends strongly on the host mass, with the AGN host mass function peaking at intermediate mass and with the AGN fraction increasing with host mass. AGNs in low-mass hosts show strong cosmic evolution in comoving number density, the fraction of such galaxies hosting active nuclei and the comoving X-ray energy density. The integrated X-ray luminosity function is used to estimate the amount of the accreted black hole mass in these AGNs and places a strong lower limit of 12% to the fraction of local low-mass galaxies hosting black holes, though a more likely value is probably much higher (> 50%) once the heavily-obscured objects missed in current X-ray surveys are accounted for.