Extremely Red Objects: an X-ray dichotomy
  We analyze the X-ray properties of a near-infrared selected (Ks < 20) sample of spectroscopically identified Extremely Red Objects (R-Ks>5) in a region of the Chandra Deep Field-South using the public 1 Ms observation. The 21 objects were classified, on the basis of deep VLT spectra, in two categories: 13 dusty star-forming galaxies showing [OII] emission, and 8 early-type galaxies with absorption features in their optical spectra. Only one emission line object has been individually detected; its very hard X-ray spectrum and the high intrinsic X-ray luminosity unambiguously reveal the presence of an obscured AGN. Stacking analysis of the remainder 12 emission line objects shows a significant detection with an average luminosity L(X)~8x10^{40} erg/s in the rest-frame 2-10 keV band. The stacked counts of the 8 passive galaxies do not provide a positive detection. We briefly discuss the implications of the present results for the estimate of the Star Formation Rate (SFR) in emission line EROs. 
M. Brusa (1,2), A. Comastri (2), E. Daddi (3), A. Cimatti (4), M.   Mignoli (2), L. Pozzetti (2) ((1) Dip. di Astronomia, Un...