[BCD2005] 180 , the SIMBAD biblio

We present the results of a deep (about 80ks) XMM-Newton survey of the largest sample of near-infrared selected Extremely Red Objects (R-K>5) available to date to K_S≲19.2. At the relatively bright X-ray fluxes (F_2-10 keV_>4x10^–15erg/cm²/s) and near-infrared magnitude probed by the present observations, the fraction of AGN (i.e. X-ray detected) among the ERO population is small (∼3.5%); conversely, the fraction of EROs among hard X-ray selected sources is much higher (∼20%). The X-ray properties of EROs detected in our XMM-Newton observation indicate absorption in excess of 10²²cm^–2 in a large fraction of them. We have also considered additional samples of X-ray detected EROs available in the literature. X-ray spectral analysis of the highest S/N sources unambiguously indicates that large columns of cold gas (even >10²³cm^–2) are the rule rather than the exception. The X-ray, optical and near-infrared properties of those X-ray selected EROs with a spectroscopic or photometric redshift nicely match those expected for type 2 quasars, the high-luminosity, high-redshift obscured AGNs predicted in baseline XRB synthesis models. A close correlation is detected between X- and K-band fluxes. For the AGN EROs this is consistent, under reasonable assumptions, with the relation established locally between the host galaxies and their central black holes. This suggests that the majority of EROs are powered by massive black holes accreting, on average, at about 0.03-0.1 of the Eddington limit.