Double-peaked profiles: ubiquitous signatures of disks in the Broad
  Emission Lines of Active Galactic Nuclei
  Broad (~10,000 km/s), 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 R~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 (M) in Type 1
AGN M(SMBH)=f [R(BLR) (Delta V)^2]/G is f = 1/[sin^2(i)] for the disk dominated
sources. Our median inclination i=27 degrees implies f=4.5, very close to the
most recent value of f=4.3+/-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.
