Using deep narrowband and broadband imaging, we identify 401 z ≈ 0.40 and 249 z ≈ 0.49 Hαline-emitting galaxies in the Subaru Deep Field. Compared to other Hαsurveys at similar redshifts, our samples are unique since they probe lower Hαluminosities, are augmented with multi-wavelength (rest-frame 1000 -1.5 μm) 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 Hβ detected above 5σ. The Balmer decrements indicate an average extinction of A(Hα) = 0.7+1.4-0.7mag. We find that the Balmer decrement systematically increases with higher Hαluminosities 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" Hαluminosity which is then reddened assuming the color excess from SED modeling. The SED-predicted Hαluminosity agrees with Hαnarrowband measurements over 3dex (rms of 0.25dex). We then use the SED SFRs to test different statistically based dust corrections for Hαand find that adopting 1mag 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 3dex (rms of 0.3dex). 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 Hαmeasurements at z ∼ 0.5. © 2012. The American Astronomical Society. All rights reserved.
