The Swift/BAT AGN Spectroscopic Survey -- IX. The Clustering Environments of an Unbiased Sample of Local AGN

TL;DR

This study analyzes the clustering environments of local AGN using the Swift/BAT survey, revealing their preference for galaxy group environments and differences based on obscuration and black hole mass.

Contribution

It provides the first large, unbiased clustering analysis of local AGN using hard X-ray selected data, linking AGN properties to their dark matter halo environments.

Findings

AGN reside in galaxy group environments

Obscured AGN are in denser environments than unobscured ones

Massive black holes are more likely in central galaxies

Abstract

We characterize the environments of local accreting supermassive black holes by measuring the clustering of AGN in the Swift/BAT Spectroscopic Survey (BASS). With 548 AGN in the redshift range 0.01<z<0.1 over the full sky from the DR1 catalog, BASS provides the largest, least biased sample of local AGN to date due to its hard X-ray selection (14-195 keV) and rich multiwavelength/ancillary data. By measuring the projected cross-correlation function between the AGN and 2MASS galaxies, and interpreting it via halo occupation distribution (HOD) and subhalo-based models, we constrain the occupation statistics of the full sample, as well as in bins of absorbing column density and black hole mass. We find that AGN tend to reside in galaxy group environments, in agreement with previous studies of AGN throughout a large range of luminosity and redshift, and that on average they occupy their dark matter halos similar to inactive galaxies of comparable stellar mass. We also find evidence that obscured AGN tend to reside in denser environments than unobscured AGN, even when samples were matched in luminosity, redshift, stellar mass, and Eddington ratio. We show that this can be explained either by significantly different halo occupation distributions or statistically different host halo assembly histories. Lastly, we see that massive black holes are slightly more likely to reside in central galaxies than black holes of smaller mass.