C-GOALS II. Chandra Observations of the Lower Luminosity Sample of Nearby Luminous Infrared Galaxies in GOALS

TL;DR

This study analyzes Chandra X-ray data for 63 lower-luminosity LIRGs in the GOALS survey, revealing AGN presence, dual AGN systems, and the spatial distribution of X-ray emission, providing insights into the nuclear activity of these galaxies.

Contribution

First detailed X-ray analysis of lower-luminosity LIRGs in GOALS, comparing AGN fractions and spatial properties with higher-luminosity counterparts.

Findings

31% of galaxies host AGN, slightly less than higher-luminosity samples.

59% of X-ray selected AGN do not dominate the galaxy’s bolometric luminosity.

Dual AGN detected in 2 systems, with a higher dual AGN fraction than previous samples.

Abstract

We analyze Chandra X-ray observatory data for a sample of 63 luminous infrared galaxies (LIRGs), sampling the lower-infrared luminosity range of the Great Observatories All-Sky LIRG survey (GOALS), which includes the most luminous infrared selected galaxies in the local universe. X-rays are detected for 84 individual galaxies within the 63 systems, for which arcsecond resolution X-ray images, fluxes, infrared and X-ray luminosities, spectra and radial profiles are presented. Using X-ray and MIR selection criteria, we find AGN in (31$\pm$5)% of the galaxy sample, compared to the (38$\pm$6)% previously found for GOALS galaxies with higher infrared luminosities (C-GOALS I). Using mid-infrared data, we find that (59$\pm$9)% of the X-ray selected AGN in the full C-GOALS sample do not contribute significantly to the bolometric luminosity of the host galaxy. Dual AGN are detected in two systems, implying a dual AGN fraction in systems that contain at least one AGN of (29$\pm$14)%, compared to the (11$\pm$10)% found for the C-GOALS I sample. Through analysis of radial profiles, we derive that most sources, and almost all AGN, in the sample are compact, with half of the soft X-ray emission generated within the inner $\sim 1$ kpc. For most galaxies, the soft X-ray sizes of the sources are comparable to those of the MIR emission. We also find that the hard X-ray faintness previously reported for the bright C-GOALS I sources is also observed in the brightest LIRGs within the sample, with $L_{\rm FIR}>8\times10^{10}$ L$_{\odot}$.