Description
We present a new measurement of the space density of high-redshift (z~3.0-4.5), X-ray-selected quasi-stellar objects (QSOs) obtained by exploiting the deep and uniform multiwavelength coverage of the COSMOS survey. We have assembled a large (40 objects), homogeneous sample of z>3 QSOs with X-ray flux F0.5-2keV>10^-15^erg/cm^2^/s, and available spectroscopic (22) or photometric (18) redshifts. We discuss their optical (color-color diagrams) and X-ray properties, their number counts and space densities and compare our findings with previous works and model predictions.
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