Role of AGNs in the Ultra-Luminous Infrared Galaxy phase since z ~ 3. (arXiv:1302.0113v1 [astro-ph.CO])

Role of AGNs in the Ultra-Luminous Infrared Galaxy phase since z ~ 3. (arXiv:1302.0113v1 [astro-ph.CO]):
In order to understand the mutual influence between active galactic nuclei
(AGN) and star formation during the evolution of galaxies, we investigate 142
galaxies detected in both X-ray and 70{\mu}m observations in the COSMOS (Cosmic
Evolution Survey) field. All of our data are obtained from archive, X-ray point
source catalogs from Chandra and XMM-Newton observation; far-infrared 70{\mu}m
point source catalog from Spitzer-MIPS observation. Although the IRAC colors of
our samples indicate the existence of star formation, the ratio of rest frame
2-10 keV luminosity to total infrared luminosity (8-1000{\mu}m) shows that AGN
predominates the spectral energy distribution (SED). We identify obscured AGN
in these 70{\mu}m luminous galaxies as characterized by a larger hardness
ratio. The higher X-ray obscuration fraction indicates an extra contribution
from the star formation in the host galaxy in addition to the usual AGN dusty
torus. If AGN feedback occurs in their host galaxies, the star formation must
be quenched and dust in host galaxy will be dispersed. However, our temperature
fitting shows there is no significant dust temperature enhancement in
far-infrared wavelength, suggesting the thermal radiative feedback is absent
from the AGN to the galaxy.