Host Galaxy Morphology and the AGN Unified Model

Abstract

We use a sample of active galaxies from the Cosmic Evolution Survey to show that host galaxy morphology is tied to the accretion rate and X-ray obscuration of its active galactic nucleus (AGN). Unobscured and rapidly accreting broad-line AGNs are more likely to be in spheroid-dominated hosts than weak or obscured AGNs, and obscured AGNs are more likely to have disturbed host galaxies. Much of the disagreement in previous work on the AGN-merger connection is likely due to each study probing AGNs with different obscuration and accretion properties. Only obscured AGNs seem to merger-driven, while weak AGNs are fed by stochastic processes in disks, and rapidly-accreting broad-line AGNs require massive bulges. Our observed "unified model" for AGN hosts fits with theoretical models for merger-driven AGN evolution, but is also consistent with steady-state AGN activity.