Broad ( \sim 10,000 km s ^ { -1 } ) , double-peaked emission-line profiles of Balmer lines emitted by active galactic nuclei ( AGN ) are thought to originate in the outer parts of an accretion disk surrounding a nuclear supermassive black hole ( SMBH ) , at \sim 1000 gravitational radii and are most frequently observed in the nuclear spectra of low-luminosity AGN ( LLAGN ) and radio-galaxies .
In the present paper we argue that broad double-peaked profiles are present also in the spectra of other Type 1 AGN , such as Seyfert 1 galaxies , suggesting that the inner part of the broad-line region ( BLR ) is also the outer part of the accretion disk .
We use the Palomar spectral survey of nearby galaxies to show that the only difference between Seyfert 1 BLR line profiles and “ bona fide ” double peakers is that , in most cases , besides a disk component , we need an additional Gaussian component attributed to non-disk clouds .
The recognition that the inner and most variable part of the BLR has a disk geometry suggests that the factor f in the expression to obtain the SMBH mass in Type 1 AGN M _ { BH } = f \left ( R _ { BLR } \Delta V ^ { 2 } / G \right ) is f = 1 / \sin ^ { 2 } i for the disk dominated sources .
Our median i = 27 ^ { \circ } implies f = 4.5 , very close to the most recent value of f = 4.3 \pm 1.05 , obtained from independent studies .
We derive a relation between f and the FWHM of the broad profile that may help to reduce the uncertainties in the SMBH mass determinations of AGN .