Star formation in bulgeless late type spiral Galaxies

M. Das1*, S. Ramya1, C. Sengupta2 and K. Mishra3
1Indian Institute of Astrophysics, Bengaluru 560034, India
2Calar Alto Observatory, Centro Astronmico Hispano Alemn, C/ Jess Durbn Remn, 2-2, 04004 Almeria, Spain
3Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA

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We present radio and follow-up optical observations of a sample of bulgeless late type spiral galaxies. We searched for signs of nuclear activity and disk star formation in the sample galaxies. Interaction induced star formation can often trigger bulge formation. We found significant radio emission associated with star formation in two sample galaxies, NGC3445 and NGC4027, both of which are tidally interacting with nearby companions. For the others, the star formation was either absent or limited to only localized regions in the disk. Both galaxies also have oval bars that are possibly pseudobulges that may later evolve into bulges. We did follow up optical H imaging and nuclear spectroscopy of NGC3445 and NGC4027 using the Himalayan Chandra Telescope (HCT). The Hα emission is mainly associated with strong spiral arms that have been triggered by the tidal interact1ions. The nuclear spectra of both galaxies indicate ongoing nuclear star formation but do not show signs of AGN activity. We thus conclude that star formation in bulgeless galaxies is generally low but is enhanced when the galaxies interact with nearby companions; this activity may ultimately lead to the formation of bulges in these galaxies.

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Keywords : galaxies: active – galaxies: bulges – galaxies: spiral – galaxies: interactions – radio continuum: galaxies