THE WYOMING SURVEY FOR Hα. II. Hα LUMINOSITY FUNCTIONS AT z ≈ 0.16, 0.24, 0.32, AND 0.40

Abstract

The Wyoming Survey for H-alpha, or WySH, is a large-area, ground-based imaging survey for H-alpha-emitting galaxies at redshifts of z ~ 0.16, 0.24, 0.32, and 0.40. The survey spans up to four square degrees in a set of fields of low Galactic cirrus emission, using twin narrowband filters at each epoch for improved stellar continuum subtraction. H-alpha luminosity functions are presented for each Delta(z) ~ 0.02 epoch based on a total of nearly 1200 galaxies. These data clearly show an evolution with lookback time in the volume-averaged cosmic star formation rate. Integrals of Schechter fits to the incompleteness- and extinction-corrected H-alpha luminosity functions indicate star formation rates per co-moving volume of 0.010, 0.013, 0.020, 0.022 h_70 M_sun yr^{-1} Mpc^{-3} at z ~ 0.16, 0.24, 0.32, and 0.40, respectively. Statistical and systematic measurement uncertainties combined are on the order of 25% while the effects of cosmic variance are at the 20% level. The bulk of this evolution is driven by changes in the characteristic luminosity L_* of the H-alpha luminosity functions, with L_* for the earlier two epochs being a factor of two larger than L_* at the latter two epochs; it is more difficult with this data set to decipher systematic evolutionary differences in the luminosity function amplitude and faint-end slope. Coupling these results with a comprehensive compilation of results from the literature on emission line surveys, the evolution in the cosmic star formation rate density over 0 < z < 1.5 is measured to be rho_dot_SFR(z) = rho_dot_SFR(0) (1+z)^{3.4+/-0.4}.