  We investigate the relationship between black hole mass and host galaxy
properties for active galaxies with the lowest black hole masses currently
known in galaxy nuclei. Hubble Space Telescope imaging confirms that the host
galaxies have correspondingly low luminosity; they are ~1 mag below L*. In
terms of morphology, ~60% of the members of the sample are disk-dominated, and
all of these are consistent with containing a bulge or (more likely)
pseudobulge, while the remainder are compact systems with no discernible disk
component. In general the compact components of the galaxies do not obey the
fundamental plane of giant elliptical galaxies and classical bulges, but rather
are less centrally concentrated at a given luminosity, much like spheroidal
galaxies. Our results strongly confirm that a classical bulge is not a
requirement for a nuclear black hole. At the same time, the observed ratio of
black hole to bulge mass is nearly an order of magnitude lower in this sample
than that seen for classical bulges. While the M-sigma relation appears to
continue to low mass, it seems that black hole-galaxy scaling relations do
depend on galaxy structure.
