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Issue A&A
Volume 420, Number 3, June IV 2004
Page(s) L23 - L26
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20040157



A&A 420, L23-L26 (2004)
DOI: 10.1051/0004-6361:20040157

Letter

Growth of massive black holes by super-Eddington accretion

T. Kawaguchi1, 2, K. Aoki3, K. Ohta4 and S. Collin1

1  LUTh/Observatoire de Paris-Meudon, 5 Place J. Janssen, 92195 Meudon, France
2  Postdoctoral Fellow of the Japan Society for the Promotion of Science
3  Subaru Telescope, National Astronomical Observatory of Japan, 650 North A'ohoku Place, Hilo, HI 96729, USA
4  Department of Astronomy, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan

(Received 17 March 2004 / Accepted 30 April 2004)

Abstract
Narrow-Line Seyfert 1 galaxies (NLS1s) and Narrow-Line quasars (NLQs) seem to amount to $\sim $10-30% of active galactic nuclei (AGNs) in the local universe. Together with their average accretion rate, we argue that a black hole (BH) growth by factor of 8-800 happens in these super-Eddington accretion phase of AGNs. Moreover, there is a possible, systematic underestimation of accretion rates (in the Eddington unit) due to an overestimation of BH mass by massive accretion discs for super-Eddington objects. If it is true, the factor of BH growth above may be larger by order(s) of magnitude. In contrast, the growth factor expected in sub-Eddington phase is only $\sim $2. Therefore, the cosmic BH growth by accretion is likely dominated by super-Eddington phase, rather than sub-Eddington phase which is the majority among AGNs.

This analysis is based on the fraction and the average accretion rate of NLS1s and NLQs obtained for $z \lesssim 0.5$. If those numbers are larger at higher redshift (where BHs were probably less grown), super-Eddington accretion would be even more important in the context of cosmic BH growth history.


Key words: accretion, accretion disks -- black hole physics -- galaxies: active -- galaxies: evolution -- galaxies: nuclei -- galaxies: Seyfert

Offprint request: T. Kawaguchi, kawaguti@optik.mtk.nao.ac.jp




© ESO 2004


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