4.7 Article

HIGH-REDSHIFT QUASARS IN THE COSMOS SURVEY: THE SPACE DENSITY OF z>3 X-RAY SELECTED QSOs

期刊

ASTROPHYSICAL JOURNAL
卷 693, 期 1, 页码 8-22

出版社

IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/693/1/8

关键词

galaxies: active; surveys; X-rays: galaxies

资金

  1. ESA Member States
  2. USA (NASA)
  3. Bundesministerium fur Wirtschaft und Technologie/Deutsches Zentrum fur Luft- und Raumfahrt (BMWI/DLR) [FKZ 50 OX 0001]
  4. Max-Planck Society
  5. XMM-Newton DLR [50-G-0502]
  6. Leibniz Prize of the Deutsche Forschungsgemeinschaft [HA 1850/28-1]
  7. ASI-INAF
  8. PRIN/MIUR [I/023/05/00, 2006-02-5203]
  9. zCOSMOS ESO Large [175.A-0839]

向作者/读者索取更多资源

We present a new measurement of the space density of high-redshift (z similar or equal to 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 F0.5-2 keV > 10(-15) erg cm(-2) s(-1), 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. 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. We find that the comoving space density of luminous (L-X greater than or similar to 10(44) erg s(-1)) QSOs declines exponentially (by an e-folding per unit redshift) in the z similar to 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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