Dust Attenuation and H-alpha Star Formation Rates of z~0.5 Galaxies
  Using deep narrow-band and broad-band imaging, we identify 401 z~0.40 and 249
z~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 1000AA--1.5 microns) 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^{+1.4}_{-0.7} 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 SFRs estimated from modeling the spectral energy distribution
(SED) is 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 narrow-band 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 one magnitude 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 argue that with SED modeling, we can derive reliable
intrinsic SFRs even in the absence of H-alpha measurements at z~0.5.
