Chandra Survey of Nearby Galaxies: an Extended Catalog

TL;DR

This paper extends a catalog of nearby galaxies observed with Chandra up to 150 Mpc, identifying X-ray AGN candidates and analyzing their properties across different galaxy types and environments.

Contribution

It provides an expanded galaxy catalog with X-ray AGN candidates and compares AGN fractions across galaxy types and group memberships.

Findings

The new catalog is 2.5 times larger than previous.

Approximately 80% of new AGN candidates have low Eddington ratios.

No significant difference in AGN fractions between galaxy types or group positions.

Abstract

She et al. (Paper I) assembled a catalog of nearby galaxies observed with the Chandra X-ray observatory, by cross-matching galaxies in the NASA Extragalactic Database (NED) within 50 Mpc and the Chandra archive. That sample has enabled searches of low-mass black holes associated with late-type, bulgeless galaxies and studies of the accretion physics related to low-luminosity active galactic nuclei (LLAGNs). Using a similar approach, here we construct an extended catalog up to 150 Mpc and make a cross-correlation with a catalog of nearby galaxy groups. The new catalog consists of 1,964 galaxies, out of which 1,692 have a redshift independent distance, 1,557 are listed in the galaxy group catalog with group properties available, and 782 are identified to be X-ray AGN candidates. Compared with the AGN sample in Paper I, the new sample is 2.5 times larger in size (782 vs. 314), with ~80% of the new members having an Eddington ratio less than 10^-4. We confirm that the conclusions based on the previous sample remain. With the new sample, we compare AGN fractions between early-type and late-type galaxies, and between central and satellite galaxies in groups, and find no significant difference. This suggests that the secular process is not the dominant mechanism feeding AGNs in the local universe.