  The correlation between the maximum rotational velocity of the disk (v_m) and
the central stellar velocity dispersion of the bulge (sigma) offers insights
into the relationship between the halo and the bulge. We have assembled
integrated H I line widths and central stellar velocity dispersions to study
the v_m-sigma relation for 792 galaxies spanning a broad range of Hubble types.
Contrary to earlier studies based on much smaller samples, we find that the
v_m-sigma relation exhibits significant intrinsic scatter and that its
zeropoint varies systematically with galaxy morphology, bulge-to-disk ratio,
and light concentration, as expected from basic dynamical considerations.
Nucleated but bulgeless late-type spiral galaxies depart significantly from the
v_m-sigma relation. While these results render questionable any attempt to
supplant the bulge with the halo as the fundamental determinant of the central
black hole mass in galaxies, the observed distribution of v_m/sigma, which
depends on both the density profile and kinematic structure of the galaxy,
offers a useful constraint on galaxy formation models. With the aid of a
near-infrared Tully-Fisher relation, we identify a population of otherwise
normal, luminous galaxies that have exceptionally low values of v_m/sigma. We
argue that a significant fraction of the H I gas in these kinematically
anomalous objects is dynamically unrelaxed, having been acquired externally
either through capture from tidal interactions or through cold accretion from
the intergalactic medium.

Astrophysics