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 ( { \lambda _ { sg } } ) as a function of various disc parameters .
We find that { \lambda _ { sg } } reaches \sim 4000 { \AA } for \alpha = 0.1 , when { \dot { M } } \gtrsim 70 ( { M _ { BH } } / 10 ^ { 7 } { M _ { \odot } } ) ^ { -1 } { L _ { Edd } / c ^ { 2 } } ( where \alpha , { \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 , { \lambda _ { sg } } is as small as \sim 1500 { \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 \sim 2 \mu m to { \lambda _ { sg } } .
Incidentally , { r _ { sg } } can be less than the photon trapping radius for { \dot { M } } \gtrsim 10 ^ { 3.3 } { L _ { 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 _ { 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 .