The X-ray emission of local luminous infrared galaxies
  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
L_IR/L_sun = 11.2, thus 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 excess hard X-ray
emission relative to that expected from star-formation that 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 K alpha emission line in the non-Seyfert LIRGs
allows us to put an upper limit to the bolometric luminosity of an obscured
AGN, L_bol <1043 erg s-1 . That is, in these galaxies, if they hosted a low
luminosity AGN, its contribution to 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%.
