2004A&A...415...47K

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_sg) of a non self-gravitating disc and the corresponding emission wavelength (λ_sg) as a function of various disc parameters. We find that λ_sg reaches ∼4000Å for α=0.1, when {dot}(M)>70(M_BH/10⁷M_☉)^–1L_Edd/c² (where α, {dot}(M), M_BH and L_Edd are, respectively, the viscosity parameter, gas accretion rate onto the central black hole (BH), the BH mass and the Eddington luminosity). Moreover, λ_sg is as small as ∼ 1500Å for α=0.001, which is the smallest α case in this study. Therefore, the window for observing the self-gravitating part of an AGN accretion disc is from ∼ 2µm to λ_sg. Incidentally, r_sg can be less than the photon trapping radius for {dot}(M)>10^3.3L_Edd/c². 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_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 Hβ and [O III] widths.