The Role of Host Galaxy for the Environmental Dependence of Active Nuclei in Local Galaxies

TL;DR

This study investigates how the host galaxy type influences the environmental dependence of active galactic nuclei (AGN) in local galaxies, revealing that AGN in S0 galaxies decrease in dense environments, unlike those in spiral galaxies.

Contribution

It provides new insights into how galaxy morphology affects AGN environmental dependence, highlighting differences between S0 and spiral host galaxies.

Findings

AGN in S0 galaxies decrease with increasing halo mass

No environmental dependence observed for AGN in spiral galaxies

Differences found in luminosity functions and obscuration fractions between galaxy types

Abstract

We discuss the environment of local hard X-ray selected active galaxies, with reference to two independent group catalogues. We find that the fraction of these AGN in S0 host galaxies decreases strongly as a function of galaxy group size (halo mass) - which contrasts with the increasing fraction of galaxies of S0 type in denser environments. However, there is no evidence for an environmental dependence of AGN in spiral galaxies. Because most AGN are found in spiral galaxies, this dilutes the signature of environmental dependence for the population as a whole. We argue that the differing results for AGN in disk-dominated and bulge-dominated galaxies is related to the source of the gas fuelling the AGN, and so may also impact the luminosity function, duty cycle, and obscuration. We find that there is a significant difference in the luminosity function for AGN in spiral and S0 galaxies, and tentative evidence for some difference in the fraction of obscured AGN.