Star formation in bulgeless late type galaxies: clues to their evolution
  We present GMRT 1280 MHz radio continuum observations and follow-up optical
studies of the disk and nuclear star formation in a sample of low luminosity
bulgeless galaxies. The main aim is to understand bulge formation and overall
disk evolution in these late type galaxies. We detected radio continuum from
five of the twelve galaxies in our sample; the emission is mainly associated
with disk star formation. Only two of the detected galaxies had extended radio
emission; the others had patchy disk emission. In the former two galaxies,
NGC3445 and NGC4027, the radio continuum is associated with star formation
triggered by tidal interactions with nearby companion galaxies. We did
follow-up Halpha imaging and nuclear spectroscopy of both galaxies using the
Himalayan Chandra Telescope (HCT). The Halpha emission is mainly associated
with the strong spiral arms. The nuclear spectra indicate ongoing nuclear star
formation in NGC3445 and NGC4027 which maybe associated with nuclear star
clusters. No obvious signs of AGN activity were detected. Although nearly
bulgeless, both galaxies appear to have central oval distortions in the R band
images; these could represent pseudobulges that may later evolve into large
bulges. We thus conclude that tidal interactions are an important means of
bulge formation and disk evolution in bulgeless galaxies; without such triggers
these galaxies appear to be low in star formation and overall disk evolution.
