Volume 535, November 2011
|Number of page(s)||20|
|Published online||17 November 2011|
The X-ray emission of local luminous infrared galaxies⋆
1 Departamento de Astrofísica, Centro de Astrobiología, CSIC/INTA, Carretera de Torrejón a Ajalvir, km 4, 28850 Torrejón de Ardoz, Madrid, Spain
2 XMM-Newton Science Operation Centre, European Space Agency, 28691 Villanueva de la Cañada, Madrid, Spain
3 Instituto de Astronomía, Universidad Nacional Autónoma de México, Apartado Postal 70-264, 04510 Mexico DF, México
4 MIT Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Avenue, NE80-6011, Cambridge, MA 02139, USA
5 Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
6 Department of Physics, Durham University, South Road, Durham, DH1 3LE, UK
Received: 6 June 2011
Accepted: 5 September 2011
We study the X-ray emission of a representative sample of 27 local luminous infrared galaxies (LIRGs). The median IR luminosity of our sample is log LIR/L⊙ = 11.2, therefore the low-luminosity end of the LIRG class is well represented. We used new XMM-Newton data as well as Chandra and XMM-Newton archive data. The soft X-ray (0.5–2 keV) emission of most of the galaxies (>80%), including LIRGs hosting a Seyfert 2 nucleus, is dominated by star-formation-related processes. These LIRGs follow the star-formation rate (SFR) versus soft X-ray luminosity correlation observed in local starbursts. We find that ~15% of the non-Seyfert LIRGs (3 out of 20) have an excessively hard X-ray emission relative to that expected from star-formation, which might indicate the presence of an obscured AGN. The rest of the non-Seyfert LIRGs follow the SFR versus hard X-ray (2–10 keV) luminosity correlation of local starbursts. The non-detection of the 6.4 keV Fe Kα emission line in the non-Seyfert LIRGs allows us to put an upper limit on the bolometric luminosity of an obscured AGN, Lbol <1043 erg s-1. That is, if these galaxies were hosting a low-luminosity AGN, its contribution to the total luminosity would be less than 10%. Finally we estimate that the AGN contribution to the total luminosity for our sample of local LIRGs is between 7% and 10%.
Key words: galaxies: active / galaxies: starburst / X-ray: galaxies
Appendices are available in electronic form at http://www.aanda.org
© ESO, 2011
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