Radio Continuum and HI study of Blue Compact Dwarf Galaxies
  The multifrequency radio continuum and 21cm HI observations of five blue
compact dwarf (BCD) galaxies, Mrk 104, Mrk 108, Mrk 1039, Mrk 1069 and I Zw 97
using the Giant Meterwave Radio Telescope (GMRT) are presented here. Radio
continuum emission at 610 MHz and 325 MHz is detected from all the observed
galaxies whereas only a few are detected at 240 MHz. In our sample, three
galaxies are members of groups and two galaxies (Mrk 1069 and I Zw 97) are
isolated galaxies. The radio emission from Mrk 104 and Mrk 108 is seen to
encompass the entire optical galaxy whereas the radio emission from Mrk 1039,
Mrk 1069, I Zw 97 is confined to massive HII regions. This, we suggest,
indicates that the star formation in the latter group of galaxies has recently
been triggered and that the environment in which the galaxy is evolving plays a
role. Star formation rates (SFR) calculated from 610 MHz emission is in the
range 0.01-0.1 M_sun/yr; this is similar to the SFR obtained for individual
star forming regions in BCDs. The integrated radio spectra of four galaxies are
modelled over the frequency range where data is available. We find that two of
the galaxies Mrk 1069 and Mrk 1039, show a turnover at low frequencies which is
well fitted by free-free absorption whereas the other two galaxies, Mrk 104 and
Mrk 108, show a power law at the lowest GMRT frequencies. The flatter spectrum,
localized star formation and radio continuum in isolated galaxies lend support
to stochastic self-propagating star formation (SSPSF). The HI observations of
four galaxies Mrk 104, Mrk 108, Mrk 1039 and Mrk 1069 show extended disks as
large as ~1.1-6 times the optical size. All the observed BCDs (except Mrk 104)
show rotating disk with a half power width of ~50-124 km/s. Solid body rotation
is common in our sample. We note that the tidal dwarf (TD) origin is possible
for two of the BCDs in our sample.
