2004/12/02 by Shuang Nan Zhang
Physics and Astronomy · #Accretion (finance) #Accretion disc #Active galactic nucleus #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Galaxies: Formation, Evolution, Phenomena #Luminosity #Luminosity function #Quasar #Sky #Torus #astro-ph
paper · pdf · doi:10.1086/427800
published as Astrophys.J. 618 (2004) L79-L82 · 10 pages, 2 figures, submitted on 2004 Oct. 20 and accepted on 2004 Dec. 1 for publication in ApJ Letters
arxiv created 2004/12/02 · openalex publication_date 2004/12/07 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The luminous electromagnetic emission from distant active galactic nuclei (AGNs) including quasars is believed to be powered by accretion onto supermassive black holes. In the standard unification model for AGNs, a dusty torus covers a significant portion of the viewing angles to the accretion disk and the black hole. The system is classified as a type I AGN if the accretion disk is viewed through the opening part; otherwise, it is called a type II AGN. Therefore, the ratio of type II to type I AGNs serves as a sensitive probe to the unification model. A surprising discovery made from several large sky coverage and/or deep AGN surveys is a significant anticorrelation between the type II fraction and the observed X-ray luminosity between 2 and 10 keV. This suggests two different luminosity functions for the two types of AGNs, thus challenging the AGN unification model. However, this observed anticorrelation is a natural consequence of the AGN unification model with only one intrinsic luminosity function if the inclination angle effects of the X-ray-emitting accretion disk are taken into account. Thus, the AGN unification model survived another critical test.