The HII Region Luminosity Function and Diffuse Hα Emission in HI-Selected Galaxies from SINGG

We use Hα observations of HI-selected galaxies from the SINGG survey (Meurer et al. 2001) to study the HII region luminosity function (HII LF) and the fraction of diffuse, warm ionized gas as a function of star formation properties and HI properties. The slope of the HII LF is robust to galaxy type, but appears to flatten for starburst galaxies, which are dominated by brighter objects. We also demonstrate the dependence of the slope on galaxy angle of inclination. The fraction of total Hα emission from the diffuse ISM appears to be anti-correlated with galaxy star formation rate per unit area, as indicated by total Hα luminosity, and it is independent of inclination angle. The latter is consistent with the much larger scale height ( ∼1 kpc) of the diffuse, warm ISM relative to the typical HII region radius.

This work was supported by NSF grant AST-0448893 and the NSF REU program at Northern Arizona University.