  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 (H-alpha) images
were obtained for all of these objects. More than half of the sample galaxies
are late-type, dwarf disks (mostly Sc and Sm galaxies). We have measured the
properties of the HII regions on H-alpha, 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 H-alpha 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 from those for typical
spiral galaxies. This discrepancy could be caused by the lowest surface
brightness galaxies having somewhat episodic star formation or by them forming
a relatively larger fraction of their stars outside of dense, massive molecular
clouds. In general, the results imply that the conditions under which star
formation occurs in lower surface brightness galaxies are different than in
more typical, higher surface brightness spiral galaxies.
