The origin of optical emission from super-Eddington accreting Active Galactic Nuclei: The case of Ton S 180

Free access article

Issue		A&A Volume 415, Number 1, February III 2004


Page(s)		47 - 54
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20034613

A&A 415, 47-54 (2004)
DOI: 10.1051/0004-6361:20034613

The origin of optical emission from super-Eddington accreting Active Galactic Nuclei: The case of Ton S 180

T. Kawaguchi^{1, 2}, A. Pierens¹ and J.-M. Huré^{1, 3}

¹ LUTh/Observatoire de Paris-Meudon et CNRS UMR 8102, Place Jules Janssen, 92195 Meudon Cedex, France
e-mail: Toshihiro.Kawaguchi@obspm.fr; Arnaud.Pierens@obspm.fr; Jean-Marc.Hure@obspm.fr
² Postdoctoral Fellow of the Japan Society for the Promotion of Science
³ Université Paris 7 Denis Diderot, 2 place Jussieu, 75251 Paris Cedex 05, France

(Received 2 May 2003 / Accepted 17 October 2003 )

Abstract
Self-gravitating accretion discs have only been studied in a few nearby objects using maser spots at the parsec-scale. We find a new spectral window for observing the self-gravitating accretion disc in super-Eddington accreting Active Galactic Nuclei (AGNs). This window is determined by calculating the outermost radius ( ${r_{\rm sg}}$ ) of a non self-gravitating disc and the corresponding emission wavelength ( ${\lambda_{\rm sg}}$ ) as a function of various disc parameters. We find that ${\lambda_{\rm sg}}$ reaches ~ $4000 ~{\rm\AA}$ for $\alpha=0.1$ , when ${\dot{M}}\gtrsim 70 \, ({M_{\rm BH}}/ 10^7 ~{M_\odot})^{-1} \, {L_{\rm Edd}/c^2}$ (where $\alpha$ , ${\dot{M}}$ , ${M_{\rm BH}}$ and ${L_{\rm Edd}}$ are, respectively, the viscosity parameter, gas accretion rate onto the central black hole (BH), the BH mass and the Eddington luminosity). Moreover, ${\lambda_{\rm sg}}$ is as small as ~ $1500 ~{\rm\AA}$ for $\alpha =0.001$ , which is the smallest $\alpha$ case in this study. Therefore, the window for observing the self-gravitating part of an AGN accretion disc is from ~ $2~ \mu$ m to ${\lambda_{\rm sg}}$ . Incidentally, ${r_{\rm sg}}$ can be less than the photon trapping radius for ${\dot{M}}\gtrsim 10^{3.3}~ {L_{\rm Edd}/c^2}$ . Namely, a self-gravitating, optically-thick, advection-dominated accretion disc is expected to appear in the extremely high accretion rate regime.

Next, we demonstrate that the Mid-Infrared to X-ray spectrum of a bright, well-studied Narrow-Line Seyfert 1 galaxy, Ton S 180, is indeed well fitted by the spectrum arising from the following three components: an inner slim disc (with a corona), an outer, self-gravitating non-Keplerian disc and a dusty torus. The total mass, BH mass plus the entire disc mass, is found to be about $(1.4 {-} 8.0)\, {M_{\rm BH}}$ . If the surface density varies with radius r in proportion to r^-0.6, the total mass is consistent with the central mass estimated by H $\beta$ and [O III] widths.

Key words: accretion, accretion disks -- radiation mechanisms: thermal -- galaxies: active -- galaxies: individual: Ton S 180 -- galaxies: nuclei -- galaxies: Seyfert

Offprint request: T. Kawaguchi, Toshihiro.Kawaguchi@obspm.fr

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