New H I observations are presented for a complete sample of 109 low-luminosity star-forming galaxies taken from the KPNO International Spectroscopic Survey (KISS), the first CCD-based wide-field objective-prism survey for emission-line galaxies. This sample consists of all star-forming galaxies with MB >-18.0 and cz < 11,000 km s-1 from the first Hα-selected survey list. The galaxies in this list lie within a 1°.3-wide strip centered on δ(B1950) = 29°30′, which spans the range α(B1950) = 12h15m to α(B1950) = 17h0m. Overall, 97 out of 109 galaxies have been detected in H I. We confirm the weak trend of increasing gas richness with decreasing luminosity found by previous authors. Gas richness is also shown to be weakly anticorrelated with metallicity. The dependence of star formation rates (SFRs) and H I gas depletion timescales on metallicity is examined. The median solar-metallicity-based SFR and gas depletion timescale are 0.16 M ⊙ yr-1 and 5 Gyr, respectively. Corrections for variations in metallicity decreases SFRs by ∼0.5 dex and increases gas depletion timescales by an average of ∼8 Gyr. The majority of galaxies in this sample still have large reservoirs of H I gas and, despite their large current star formation rates, could have formed stars in a quasi-continuous manner for a Hubble time. Finally, we present the first H I mass function for low-luminosity star-forming galaxies and show that this subpopulation contributes 10%-15% of the overall H I density in the local universe. We conclude that if the H I mass function of the universe does indeed have a steeply rising low-mass slope, as suggested by previous authors, it is not due to the population of low-luminosity star-forming galaxies. Comparison with the H I mass function number densities from H I blind surveys in the range 10 8 M⊙ < MHI < 109 M ⊙ implies that 25%-50% of galaxies in this mass regime are currently undergoing a strong episode of star formation.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science