AAS 200th meeting, Albuquerque, NM, June 2002
Session 43. Galaxies
Display, Tuesday, June 4, 2002, 10:00am-6:30pm, SW Exhibit Hall

## [43.03] Star Formation Properties of HI Selected Galaxies I. Overall properties

J. F. Helmboldt, R. A. M. Walterbos (NMSU), G. D. Bothun (U. of Oregon), K. O'Neil (NAIC/Cornell), W. J. G. de Blok (ATNF)

A sample of ~120 galaxies was chosen from the H{\sc i} Parkes All Sky Survey (H{\sc i}PASS) to deduce details about star formation in nearby disk galaxies with no bias to optical surface brightness selection effects. Broad (B and R) and narrow band (H\alpha) photometry was obtained for 69 of these. The sample is dominated by late-type, dwarf disks (mostly Sc and Sm galaxies) with exponential disk scalelengths around 1 kpc or less. Both the optical and neutral hydrogen properties of these galaxies resemble those of a comparison sample of 35 low surface brightness (LSB) galaxies selected from the literature. They exhibit a weak trend between H\alpha flux per unit area and B-band surface brightness and between gas-to-light ratio (MHI/LB) and B-band central surface brightness. The star formation rates (SFRs) derived from the integrated H\alpha luminosities show that most of the galaxies have SFRs ~0.01-0.1 M\odot yr-1. Many of the galaxies have H\alpha equivalent widths, colors, and gas-to-light ratios that are difficult to explain with simple star formation histories, such as "steady state" models of exponentially decaying star formation rates.Instead, their relatively blue colors, luminosities, and current star formation rates seem more consistent with irregular star formation histories.