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

¹ ICREA and Institut de Ciències del Cosmos (ICC), Universitat de Barcelona (IEEC-UB), Martí i Franquès, 1, 08028 Barcelona, Spain
e-mail: kazushi.iwasawa@icc.ub.edu
² Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, Hawaii 96822, USA
³ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
⁴ SAO Predoctoral Fellow, Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
⁵ Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125, USA
⁶ Department of Astronomy, University of Virginia, 530 McCormick Road, Charlottesville, VA 22904 and NRAO, 520 Edgemont Road, Charlottesville, VA 22903, USA
⁷ Max Planck Institut für extraterrestrische Physik, Gießenbachstraße, 85748 Garching, Germany
⁸ IPAC, California Institute of Technology, Pasadena, CA 91125, USA
⁹ Department of Physics and Astronomy, State University of New York at Stony Brook, NY 11794, USA
¹⁰ Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK

Received: 23 June 2010
Accepted: 25 February 2011

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 (L_ir/L_⊙) ≥ 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 [Ne v]λ14.3   μm 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.