Supermassive Black Hole Accretion History Inferred from a Large Sample of [ITAL]CHANDRA[/ITAL][ITAL]Chandra[/ITAL] Hard X-Ray Sources

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Abstract
We describe the optical, near-infrared, and radio properties of a hard (2–7 keV) X-ray–selected sample detected in a deep Chandra observation of the field surrounding the Abell 370 cluster. We combine these data with similar observations of the Chandra Deep Field North and the Hawaii Survey Field SSA 13 to obtain a hard X-ray–selected sample of 69 sources with extremely deep 20 cm and optical imaging data. We have spectroscopic redshifts for 45 of the 69 sources. We find that about 4% of the greater than L* galaxy population is X-ray luminous at any time and hence that black hole accretion has a duration of about half a gigayear. We find that about 30% of the summed 2–7 keV flux from the total sample is from sources at z 1. We estimate upper bounds on the bolometric luminosities of accretion onto the supermassive black holes, from which we determine maximal mass inflow rates that increase from ~0.01 M⊙ yr-1 at z 0.5 up to ~10 M⊙ yr-1 at z 1, assuming a canonical radiative efficiency ~ 0.1. The time history of the accretion rate density is evaluated; its maximal integrated value is ρBH = 6 × 10-35 g cm-2, which is reasonably consistent with the value inferred from the local black hole mass–to–bulge mass ratio.
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