Journal Article

Accretion, growth of supermassive black holes, and feedback in galaxy mergers

Li-Xin Li

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 424, issue 2, pages 1461-1470
Published in print August 2012 | ISSN: 0035-8711
Published online August 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.21336.x
Accretion, growth of supermassive black holes, and feedback in galaxy mergers

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Abstract

Super-Eddington accretion is very efficient in growing the mass of a black hole: in a fraction of the Eddington time its mass can grow to an arbitrary large value if the feedback effect is not taken into account. However, since super-Eddington accretion has a very low radiation efficiency, people have argued against it as a major process for the growth of the black holes in quasars since observations have constrained the average accretion efficiency of the black holes in quasars to be ≳0.1. In this paper, we show that the observational constraint does not need to be violated if the black holes in quasars have undergone a two-phase growing process: with a short super-Eddington accretion process they get their masses inflated by a very large factor until the feedback process becomes important, then with a prolonged sub-Eddington accretion process they have their masses increased by a factor of ≳ 2. The overall average efficiency of this two-phase process is then ≳ 0.1, and the existence of black holes of masses ∼109 M by redshift 6 is easily explained. An observational test of the existence of the super-Eddington accretion phase is briefly discussed.

Keywords: accretion, accretion discs; black hole physics; galaxies: active; quasars: general; cosmology: miscellaneous

Journal Article.  8375 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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