C-GOALS: Chandra observations of a complete sample of luminous infrared galaxies from the IRAS Revised Bright Galaxy Survey

TL;DR

This study presents Chandra X-ray observations of a complete sample of luminous infrared galaxies, revealing the prevalence of active galactic nuclei and starburst activity, and providing insights into their merger stages and X-ray properties.

Contribution

First comprehensive X-ray analysis of a complete local LIRG sample, identifying AGN presence and characteristics in relation to galaxy mergers and starburst activity.

Findings

37% of LIRGs host AGN, increasing to 48% with mid-IR data

Double AGN detected only in NGC 6240 among systems studied

Most galaxies show extended soft X-ray emission linked to starburst outflows

Abstract

We present X-ray data for a complete sample of 44 luminous infrared galaxies (LIRGs), obtained with the Chandra X-ray Observatory. These are the X-ray observations of the high luminosity portion of the Great Observatory All-sky LIRG Survey (GOALS), which includes the most luminous infrared selected galaxies, log (Lir/Lsun) > 11.73, in the local universe, z < 0.088. X-rays were detected from 43 out of 44 objects, and their arcsec-resolution images, spectra, and radial brightness distributions are presented. With a selection by hard X-ray colour and the 6.4 keV iron line, AGN are found in 37% of the objects, with higher luminosity sources more likely to contain an AGN. These AGN also tend to be found in late-stage mergers. The AGN fraction would increase to 48% if objects with mid-IR [Ne V] detection are included. Double AGN are clearly detected only in NGC 6240 among 24 double/triple systems. Other AGN are found either in single nucleus objects or in one of the double nuclei at similar rates. Objects without conventional X-ray signatures of AGN appear to be hard X-ray quiet, relative to the X-ray to far-IR correlation for starburst galaxies, as discussed elsewhere. Most objects also show extended soft X-ray emission, which is likely related to an outflow from the nuclear region, with a metal abundance pattern suggesting enrichment by core collapse supernovae, as expected for a starburst.