  UGC 4483 is a nearby Blue Compact Dwarf (BCD) galaxy. HST observations have
resolved the galaxy into single stars and this has led to the derivation of its
star formation history and to a direct estimate of its stellar mass. We have
analysed archival VLA observations of the 21 cm line and found that UGC 4483
has a steeply-rising rotation curve which flattens in the outer parts at a
velocity of ~20 km/s. Radial motions of ~5 km/s may also be present. As far as
we know, UGC 4483 is the lowest-mass galaxy with a differentially rotating HI
disk. The steep rise of the rotation curve indicates that there is a strong
central concentration of mass. We have built mass models using the HST
information on the stellar mass to break the disk-halo degeneracy: old stars
contribute ~50$%$ of the observed rotation velocity at 2.2 disk scale-lengths.
Baryons (gas and stars) constitute an important fraction of the total dynamical
mass. These are striking differences with respect to typical dwarf irregular
galaxies (dIrrs), which usually have slowly-rising rotation curves and are
thought to be entirely dominated by dark matter. BCDs appear to be different
from non-starbursting dIrrs in terms of their HI and stellar distributions and
their internal dynamics. To their high central surface brightnesses and high
central HI densities correspond strong central rotation-velocity gradients.
This implies that the starburst is closely related with the gravitational
potential and the concentration of gas. We discuss the implications of our
results on the properties of the progenitors/descendants of BCDs.
