Star formation at the extreme ends of the Hubble sequence

I present the results of two different studies aimed at exploring star formation within galaxies at the two extreme ends of the Hubble sequence and how they may contribute to our knowledge of galaxy evolution and star formation. The first of these two projects uses broad-band (B and R) and narrow-band (Ha) imaging of 69 galaxies drawn from a single-dish HI survey (the HI Parkes All Sky Survey) to examine star formation in a galaxy sample that is not biased against late-type, low surface brightness galaxies. The results imply that while a bias toward higher surface brightness galaxies may cause flux limited optically selected catalogs to miss more than 10% of the total galaxy number density, they will only miss about 3-4% of the total star formation rate density. However, the lower surface brightness galaxies in this sample have HII region and diffuse ionized gas properties that imply that they may provide interesting examples of star formation occurring under extreme conditions.

The second project uses a sample of ~37,000 early-type galaxies culled from the Sloan Digital Sky Survey to identify a subsample of actively star forming early-type galaxies with the aim of exploring the properties of their star forming regions. Both the existence and level of star formation activity appears to strongly depend on gas-richness. It was also found that a higher fraction of star forming early-type galaxies reside in lower density environments. The sample was also used to explore the possibility that the star formation within these early-type galaxies can convert them into post-starburst E+A galaxies. The general properties and environments of the star forming early-type galaxies match those of E+A galaxies. The results of detailed population synthesis modeling also indicate that the most actively star for ming early-type galaxies will most likely become E+A galaxies. Narrow- and broad- band imaging of a small subset of galaxies revealed that the star formation is centralized can increase the bulge fraction by ~6%.