High redshift quasars in the COSMOS survey: the space density of z>3 X-ray selected QSOs

Details High redshift quasars in the COSMOS survey: the space density of z>3 X-ray selected QSOs High redshift quasars in the COSMOS survey: the space density of z>3 X-ray selected QSOs

2008-09-15

arxiv.org/abs/0809.2513v1

Astronomy and Astrophysics

Astrophysics

36 pages, 9 figures, 4 tables. To appear on ApJ, version revised according to referee comments

Scientific paper

10.1088/0004-637X/693/1/8

We present a new measurement of the space density of high redshift (3.010^{-15} cgs), homogeneous sample of z>3 QSOs for which spectroscopic (22) or photometric (18) redshifts are available. We present the optical (color-color diagrams) and X-ray properties, the number counts and space densities of the z>3 X-ray selected quasars population and compare our findings with previous works and model predictions. We find that the optical properties of X-ray selected quasars are not significantly different from those of optically selected samples. There is evidence for substantial X-ray absorption (logN_H>23 cm^{-2}) in about 20% of the sources in the sample. The comoving space density of luminous (L_X >10^{44} erg s^-1) QSOs declines exponentially (by an e--folding per unit redshift) in the z=3.0-4.5 range, with a behavior similar to that observed for optically bright unobscured QSOs selected in large area optical surveys. Prospects for future, large and deep X-ray surveys are also discussed.

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