Dwarf Seyfert 1 Nuclei and the Low-Mass End of the M-sigma Relation
  To examine the relationship between black hole mass and host galaxy velocity dispersion for low black hole masses, we have measured the velocity dispersions of 15 Seyfert 1 galaxies from the catalog of Greene & Ho (2004). These Seyferts were selected from the Sloan Digital Sky Survey to have estimated black hole masses below 10^6 solar masses. The data are consistent with a straightforward downward extrapolation of the local M-sigma relation, indicating that this correlation extends over a range of more than four orders of magnitude in black hole mass. The rms scatter of the sample about the extrapolated M-sigma relation is 0.57 dex, consistent with the expected scatter of single-epoch mass estimates for Seyfert 1 galaxies. 
A.J. Barth, J.E. Greene, L.C. Ho