XMM-COSMOS Catalog of Optical/IR Counterparts

Thanks to the redshift completeness (almost 100%) the authors were able to constrain the high-luminosity tail of the X-ray luminosity function confirming that the peak of the number density of log L<sub>X</sub> > 44.5 active galactic nuclei (AGNs) is at z ~ 2. Spectroscopically identified obscured and unobscured AGNs, as well as normal and star-forming galaxies, present well-defined optical and infrared properties.

The authors devised a robust method to identify a sample of ~150 high-redshift (z > 1), obscured AGN candidates for which optical spectroscopy is not available. They were able to determine that the fraction of the obscured AGN population at the highest (L<sub>X</sub> > 10<sup>44</sup> erg s<sup>-1</sup>) X-ray luminosity is ~15%-30% when selection effects are taken into account, providing an important observational constraint for X-ray background synthesis.

The authors studied in detail the optical spectrum and the overall spectral energy distribution of a prototypical Type 2 QSO (source number 2028), caught in a stage transitioning from being starburst dominated to AGN dominated, which was possible to isolate only thanks to the combination of X-ray and infrared observations. This table was created by the HEASARC in July 2010 based on the electronic version of Table 2 from the paper which was obtained from the Astrophysical Journal web site. <p> The HEASARC has made some changes to this material in order to make it more compliant with CDS/IAU Nomenclature and HEASARC table standards: <p> (i) The original naming convention suggested by the authors used a prefix of 'XMMC_' and the J2000.0 RA and Dec position in decimal degrees to 10<sup>-5</sup> degrees precision, e.g., XMMC_150.10515+1.98082'; the HEASARC has replaced these names by alternative new ones (in the alt_name parameter) of the form 'XMMU JHHMMSS.s+DDMMSS' where the prefix is the usual one for XMM-Newton sources and the remainder of the field is the J2000.0 equatorial coordinates truncated to 0.1 seconds of time in RA and to 1 arcsecond in Declination; <p> (ii) We have used for the alt_name parameter the naming convention recommended by the Dictionary of Nomenclature of Celestial Objects for XMM-COSMOS sources, viz. the "XMMC' prefix and the source (XID) number, e.g., "XMMC 2028'.

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