When Supermassive Black Holes Were Growing: Clues from Deep X-ray Surveys
Abstract
Merging the Chandra and XMM-Newton deep surveys with the previously identified ROSAT surveys a unique sample of almost 1000 AGN-1 covering five orders of magnitude in 0.5-2 keV flux limit and six orders of magnitude in survey solid angle with ~95% completeness has been constructed. The luminosity-redshift diagram is almost homogeneously filled. AGN-1 are by far the largest contributors to the soft X-ray selected samples. Their evolution is responsible for the break in the total 0.5-2 keV source counts. The soft X-ray AGN-1 luminosity function shows a clear change of shape as a function of redshift, confirming earlier reports of luminosity-dependent density evolution for optical quasars and X-ray AGN. The space density evolution with redshift changes significantly for different luminosity classes, showing a strong positive evolution, i.e. a density increase at low redshifts up to a certain redshift and then a flattening. The redshift, at which the evolution peaks, changes considerably with X-ray luminosity, from z≈0.5-0.7 for luminosities log Lx=42-43 erg s-1 to z≈2 for log Lx=45-46 erg s-1. The amount of density evolution from redshift zero to the maximum space density also depends strongly on X-ray luminosity, more than a factor of 100 at high luminosities, but less than a factor of 10 for low X-ray luminosities. For the first time, a significant decline of the space density of X-ray selected AGN towards high redshift has been detected in the range log Lx=42-45 erg s-1, while at higher luminosities the survey volume at high-redshift is still too small to obtain meaningful densities. A comparison between X-ray and optical properties shows now significant evolution of the X-ray to optical spectral index for AGN-1. The constraints from the AGN luminosity function and evolution in comparison with the mass function of massive dark remnants in local galaxies indicates, that the average supermassive black hole has built up its mass through efficient accretion (ɛ~10%) and is likely rapidly spinning.
- Publication:
-
Growing Black Holes: Accretion in a Cosmological Context
- Pub Date:
- 2005
- DOI:
- 10.1007/11403913_78
- arXiv:
- arXiv:astro-ph/0412576
- Bibcode:
- 2005gbha.conf..418H
- Keywords:
-
- X-Ray Surveys;
- Supermassive Black Holes;
- Astrophysics
- E-Print:
- Proceedings of the Conference "Growing Black Holes"