The rotation curves shapes of late-type dwarf galaxies
  We present rotation curves derived for a sample of 62 late-type dwarf
galaxies that have been observed as part of the Westerbork HI Survey of Spiral
and Irregular Galaxies (WHISP) project. The rotation curves were derived by
interactively fitting model data cubes to the observed cubes, taking rotation
curve shape, HI distribution, inclination, and the size of the beam into
account. This makes it possible to correct for the effects of beam smearing.
The dwarf galaxies in our sample have rotation-curve shapes that are similar to
those of late-type spiral galaxies, in the sense that their rotation curves,
when expressed in units of disk scale lengths, rise as steeply in the inner
parts and start to flatten at two disk scale lengths. None of the galaxies in
our sample have solid-body rotation curves that extend beyond three scale
lengths. The logarithmic outer rotation curve slopes are similar between
late-type dwarf and spiral galaxies. Thus, whether the flat part of the
rotation curve is reached seems to depend more on the extent of the rotation
curve than on its amplitude. We also find that the outer rotation curve shape
does not strongly depend on luminosity, at least for galaxies fainter than
M_R~-19. We find that in spiral galaxies and in the central regions of
late-type dwarf galaxies, the shape of the central distribution of light and
the inner rise of the rotation curve are related. This implies that galaxies
with stronger central concentrations of light also have higher central mass
densities, and it suggests that the luminous mass dominates the gravitational
potential in the central regions, even in low surface brightness dwarf
galaxies.
