DUST ATTENUATION AND Hα STAR FORMATION RATES OF z ∼ 0.5 GALAXIES

Using deep narrowband and broadband imaging, we identify 401 z approximate to 0.40 and 249 z approximate to 0.49 H alpha line-emitting galaxies in the Subaru Deep Field. Compared to other H alpha surveys at similar redshifts, our samples are unique since they probe lower H alpha luminosities, are augmented with multi-wavelength (rest-frame 1000 angstrom-1.5 mu m) coverage, and a large fraction (20%) of our samples has already been spectroscopically confirmed. Our spectra allow us to measure the Balmer decrement for nearly 60 galaxies with H beta detected above 5 sigma. The Balmer decrements indicate an average extinction of A(H alpha) = 0.7(-0.7)(+1.4) mag. We find that the Balmer decrement systematically increases with higher H alpha luminosities and with larger stellar masses, in agreement with previous studies with sparser samples. We find that the star formation rates (SFRs) estimated from modeling the spectral energy distribution (SED) are reliable-we derived an "intrinsic" H alpha luminosity which is then reddened assuming the color excess from SED modeling. The SED-predicted H alpha luminosity agrees with H alpha narrowband measurements over 3 dex (rms of 0.25 dex). We then use the SED SFRs to test different statistically based dust corrections for H alpha and find that adopting 1 mag of extinction is inappropriate: galaxies with lower luminosities are less reddened. We find that the luminosity-dependent dust correction of Hopkins et al. yields consistent results over 3 dex (rms of 0.3 dex). Our comparisons are only possible by assuming that stellar reddening is roughly half of nebular reddening. The strong correspondence argues that with SED modeling, we can derive reliable intrinsic SFRs even in the absence of H alpha measurements at z similar to 0.5.