X-ray QSO evolution from a very deep ROSAT survey
Abstract
In the deepest optically identified X-ray survey yet performed, we have identified 32 X-ray selected QSOs to a flux limit of 2x10^{-15} erg cm^{-2} s^{-1} (0.5-2 keV). The survey, performed with the ROSAT PSPC, has 89% spectroscopic completeness. The QSO log(N)-log(S) relation is found to have a break to a flat slope at faint fluxes. The surface density of QSOs at the survey limit is 230+/-40 per square degree, the largest so far of any QSO survey. We have used this survey to measure the QSO X-ray luminosity function at low luminosities (Lx<10^{44.5} erg s^{-1}) and high redshifts (1<z<2.5). The highest redshift QSO in the survey has z=3.4. Combined with the QSOs from the Einstein EMSS at bright fluxes, we find pure luminosity evolution of the form Lx proportional to (1+z)^{3.0(+0.2,-0.3)} is an adequate description of the evolution of the X-ray luminosity function at low redshifts. A redshift cutoff in the evolution is required at z=1.4 ^{+0.4}_{-0.17} (for qo=0.5). We discuss the form of this evolution, its dependence on the model assumed and the errors on the derived parameters. We show that most previous X-ray surveys, including the EMSS, are consistent with a power law luminosity evolution index of 3.0. The contribution of QSOs to the 1-2 keV cosmic X-ray background is found to be between 31% and 51%.
Keywords
Cite
@article{arxiv.astro-ph/9610124,
title = {X-ray QSO evolution from a very deep ROSAT survey},
author = {L. R. Jones and I. M. McHardy and M. R. Merrifield and K. O. Mason and P. J. Smith and R. G. Abraham and G. Branduardi-Raymont and A. M. Newsam and G. Dalton and M. Rowan-Robinson and G. Luppino},
journal= {arXiv preprint arXiv:astro-ph/9610124},
year = {2015}
}
Comments
12 pages, 5 postscript figures, uses mnras.sty, to be published in MNRAS