The hard X-ray emission of luminous infrared galaxies
Abstract
We present a study of the hard X-ray properties of a sample that includes all the Luminous Infrared Galaxies (LIGs, LIR > 1011 L_sun) observed in the 2-10 keV energy band (new and archival data). We find that a significant fraction of the sources optically classified as AGNs do not show any indication of nuclear activity in the X rays, thus suggesting heavy absorption along our line of sight. The absence of strong emission in the 20-200 keV band in a subsample of LIGs observed with BeppoSAX suggests that in many cases these sources are completely Compton thick (N_H > 1025 cm-2). From a comparison between the infrared and the X-ray emission we deduce that the mid-IR emission is absorbed by a lower column density than the X-ray emission or, alternatively, that the dust-to-gas ratio is lower than Galactic. We describe a simple model that reproduces the IR-X correlation by means of mixed AGN and starburst contributions and we compare the predictions of this model with the observational data at X-ray and optical wavelengths. Finally, we discuss the biases that affect the currently available samples of LIGs and briefly analyze a small unbiased sample, finding that at least 50% of the sources host a (weak) AGN.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- May 2000
- DOI:
- 10.48550/arXiv.astro-ph/0002460
- arXiv:
- arXiv:astro-ph/0002460
- Bibcode:
- 2000A&A...357...13R
- Keywords:
-
- GALAXIES: ACTIVE;
- GALAXIES: STARBURST;
- INFRARED: GALAXIES;
- X-RAYS: GALAXIES;
- Astrophysics
- E-Print:
- 12 LaTeX pages including 6 postscript figures. Accepted for publication in A&