ar X iv : a st ro - p h / 05 06 03 9 v 1 1 J un 2 00 5 Star Formation in H i Selected Galaxies . II . HII Region Properties

A sample of 69 galaxies with radial velocities less than 2500 km s was selected from the Hi Parkes All Sky Survey (HiPASS) to deduce details about star formation in nearby disk galaxies selected with no bias to optical surface brightness selection effects. Broad (B and R) and narrow band (Hα) images were obtained for all of these objects. More than half of the sample galaxies are latetype, dwarf disks (mostly Sc and Sm galaxies). We have measured the properties of the Hii regions on Hα, continuum subtracted images, using the HIIphot package developed by Thilker et al. (2000). All but one of the galaxies contained at least one detectable Hii region. Examination of the properties of the Hii regions in each galaxy revealed that the brightest regions in higher surface brightness galaxies tend to be more luminous than those in lower surface brightness galaxies. A higher fraction (referred to as the diffuse fraction) of the Hα emission from lower surface brightness galaxies comes from diffuse ionized gas (DIG). Hii region luminosity functions (LFs) co-added according to surface brightness show that the shapes of the LFs for the lowest surface brightness galaxies are different Department of Astronomy, New Mexico State University, Dept. 4500 PO Box 30001 Las Cruces, NM 88003 Department of Physics, University of Oregon, Eugene, Oregon 97403 NRAO, P.O. Box 2 Green Bank, WV 24944