UV/Hα Turmoil

Abstract

A great deal of our understanding of star formation in the local universe has been built upon an extensive foundation of Hα observational studies. However, recent work in the ultraviolet (UV) with GALEX has shown that star formation rates (SFRs) inferred from Hα in galactic environments characterized by low stellar and gas densities tend to be less than those based on the UV luminosity. The origin of the discrepancy is actively debated because one possible explanation is that the stellar initial mass function is systematically deficient in high mass stars in such environments. In this contribution, we summarize our work on this topic using a dwarf galaxy dominated sample of ~ 300 late-type galaxies in the 11 Mpc Local Volume. The sample allows us to examine the discrepancy between Hα and UV SFRs using a statistical number of galaxies with activities less than 0.1 M_⨀ yr^-1 A range of potential causes for such an effect are reviewed. We find that while the IMF hypothesis is not inconsistent with our observations, alternate explanations remain that must be investigated further before a final conclusion can be drawn.