Star formation density and H alpha luminosity function of an emission-line-selected galaxy sample at z similar to 0.24

We use narrow-band imaging (full width at half-maximum = 70 angstrom) to select a sample of emission-line galaxies between 0.20 less than or similar to z less than or similar to 1.22 in two fields covering 0.5 deg(2). We use spectroscopic follow-up to select a subsample of H alpha-emitting galaxies at z similar to 0.24 and determine the H alpha luminosity function and star formation density at z similar to 0.24 for both of our fields. Corrections are made for imaging and spectroscopic incompleteness, extinction and interloper contamination on the basis of the spectroscopic data. When compared to each other, we find the field samples differ by Delta alpha = 0.2 in faint-end slope and Delta log [L* (erg s(-1))] = 0.2 in luminosity. In the context of other recent surveys, our sample has comparable faint-end slope, but a fainter L* turnover. We conclude that systematic uncertainties and differences in selection criteria remain the dominant sources of uncertainty between Ha luminosity functions at this redshift. We also investigate average star formation rates as a function of local environment and find typical values consistent with the field densities that we probe, in agreement with previous results. However, we find tentative evidence for an increase in star formation rate with respect to the local density of star-forming galaxies, consistent with the scenario that galaxy-galaxy interactions are triggers for bursts of star formation.