The hard X-ray view of bright infrared galaxies
  Aims. The synthesis of the cosmic X-ray background (CXB) requires a large
population of Compton-thick active galactic nuclei that have not been detected
so far. We probe whether bright infrared galaxies could harbor a population of
Compton-thick nuclei and if they could contribute significantly. Methods. We
analyzed 112 Msec of INTEGRAL observations obtained on 613 galaxies from the
IRAS Revised Bright Galaxy Sample. We derived the average hard X-ray (18-80
keV) emission of Seyfert and various non Seyfert galaxy subsamples to estimate
their relative contribution to the locally emitted CXB. Results. The Seyfert 1
& 2 are detected at hard X-rays. None of the other galaxy subsamples were
detected. ULIRGs are at least 5 times under-luminous at hard X-rays when
compared to Seyferts. The upper limit obtained for the average non Seyfert
galaxies is as low as 7E-13 erg/s cm2. On average, these galaxies do not
contain active nuclei brighter than 10E41 erg/s at hard X-rays. The total hard
X-ray flux detected from the sample is 4.9E-9 erg/s cm2 (about 1% of the CXB),
and 64% of this originates in absorbed active nuclei. Local non-Seyfert
galaxies contribute for less than 7% and do not harbor the Compton-thick nuclei
assumed to synthesize the locally emitted CXB.
