2003/01/13 by L. L. Cowie, A. J. Barger, M. W. Bautz +2 · 8 citations
Physics and Astronomy · #Accretion (finance) #Astrophysical Phenomena and Observations #Astrophysics and Cosmic Phenomena #Galaxies: Formation, Evolution, Phenomena #Hubble Deep Field #Luminosity #Luminosity function #Observatory #ROSAT #Redshift #Supermassive black hole #astro-ph
paper · pdf · doi:10.1086/368404
published as Astrophys.J. 584 (2003) L57-L60 · 5 pages, accepted by The Astrophysical Journal Letters
arxiv created 2003/01/13 · openalex publication_date 2003/02/20 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The high angular resolution and sensitivity of the Chandra X-Ray Observatory has yielded large numbers of faint X-ray sources with measured redshifts in the soft-energy (0.5-2 keV) and hard-energy (2-8 keV) bands. Many of these sources show few obvious optical signatures of active galactic nuclei (AGNs). We use Chandra observations of the Hubble Deep Field-North region, A370, and the Hawaii Survey fields SSA 13 and SSA 22, together with the ROSAT Ultra Deep Survey soft sample and the ASCA Large Sky Survey hard sample, to construct rest-frame 2-8 keV luminosity functions versus redshift for all the X-ray sources, regardless of their optical AGN characteristics. At z = 0.1-1, most of the 2-8 keV light density arises in sources with luminosities in the 10 42 -10 44 ergs s -1 range. We show that the number density of sources in this luminosity range is rising, or is at least constant, with decreasing redshift. Broad-line AGNs are the dominant population at higher luminosities, and these sources show the well-known rapid positive evolution with increasing redshift to z ~ 3. We argue that the dominant supermassive black hole formation has occurred at recent times in objects with low accretion mass flow rates rather than at earlier times in more X-ray-luminous objects with high accretion mass flow rates.