Black hole growth and starburst activity at z = 0.6-4 in the Chandra
  Deep Field South. Host galaxies properties of obscured AGN
  The co-evolution of host galaxies and the active black holes which reside in
their centre is one of the most important topics in modern observational
cosmology. Here we present a study of the properties of obscured Active
Galactic Nuclei (AGN) detected in the CDFS 1Ms observation and their host
galaxies. We limited the analysis to the MUSIC area, for which deep K-band
observations obtained with ISAAC@VLT are available, ensuring accurate
identifications of the counterparts of the X-ray sources as well as reliable
determination of photometric redshifts and galaxy parameters, such as stellar
masses and star formation rates. In particular, we: 1) refined the
X-ray/infrared/optical association of 179 sources in the MUSIC area detected in
the Chandra observation; 2) studied the host galaxies observed and rest frame
colors and properties. We found that X-ray selected (L_X>10^{42} erg s^{-1})
AGN show Spitzer colors consistent with both AGN and starburst dominated
infrared continuum; the latter would not have been selected as AGN from
infrared diagnostics. The host galaxies of X-ray selected obscured AGN are all
massive (M_*>10^{10} M_sun) and, in 50% of the cases, are also actively forming
stars (1/SSFR<t_{Hubble}) in dusty environments. The median L/LEdd value of the
active nucleus is between 2% and 10% depending on the assumed M_{BH}/M_{*}
ratio. Finally, we found that the X-ray selected AGN fraction increases with
the stellar mass up to a value of ~30% at z>1 and M_*>3x10^{11} M_sun, a
fraction significantly higher than in the local Universe for AGN of similar
luminosities.
