Vincenzo Mainieri

MPE Garching, Germany

Poster Title: Beyond the spectroscopic limit in the GOODS/CDFS survey

Abstract: We present a detailed study of the X-ray/optical/near-IR properties and redshift distribution of the X-ray sources in the Chandra Deep Field South Survey with optical counterparts fainter than R> 25. These magnitudes are beyond the spectroscopic limit also for 10 m ground based optical telescopes. Optically faint sources represent ~25% of the whole X-ray population in the CDF-S. We use the unique multi-wavelength follow up of the GOODS survey and the recently released UDF data. Adding the derived photometric redshifts for these faint sources in the redshift distribution we are able to attenuate the disagreement with the prediction of synthesis models of the X-ray Background but not to solve it. Therefore it is mandatory to include in synthesis models a new X-ray luminosity function of unobscured AGN. The Optically faint sources are mainly X-ray absorbed AGN ( ~83% have NH>10^22 cm-2). Many of these faint sources have high (>10) X-ray-to-optical flux ratios and we find that half of them are well fitted with a SED of an elliptical galaxy with ~ 1.5 and the remaining half with irregular or starburst galaxies often at z_phot>3. We quantify in 17% the fraction of Type II QSOs between the Optically faint sources. The overall population of Type II QSOs contribute to the [2-10] keV X-ray Background(XRB) for a fraction of ~11% while current synthesis models of the XRB predict a ~38% contribution.

Link to poster: N/A