Formation and evolution of blue compact dwarfs: The origin of their
  steep rotation curves
  The origin of the observed steep rotation curves of blue compact dwarf
galaxies (BCDs) remains largely unexplained by theoretical models of BCD
formation. We therefore investigate the rotation curves in BCDs formed from
mergers between gas-rich dwarf irregular galaxies based on the results of
numerical simulations for BCD formation. The principal results are as follows.
The dark matter of merging dwarf irregulars undergoes a central concentration
so that the central density can become up to six times higher than those of the
initial dwarf irregulars. However, the more compact dark matter halo alone can
not reproduce the gradient differences observed between dwarf irregulars and
BCDs. We provide further support that the central concentration of gas due to
rapid gas-transfer to the central regions of dwarf--dwarf mergers is
responsible for the observed difference in rotation curve gradients. The BCDs
with central gas concentration formed from merging can thus show steeply rising
rotation curves in their central regions. Such gas concentration is also
responsible for central starbursts of BCDs and the high central surface
brightness and is consistent with previous BCD studies. We discuss the
relationship between rotational velocity gradient and surface brightness, the
dependence of BCD rotation curves on star formation threshold density,
progenitor initial profile, interaction type and merger mass ratio, as well as
potential evolutionary links between dwarf irregulars, BCDs and compact dwarf
irregulars.
