THE MOSDEF SURVEY: MEASUREMENTS OF BALMER DECREMENTS AND THE DUST ATTENUATION CURVE AT REDSHIFTS z ∼ 1.4-2.6

We present results on the dust attenuation curve of z similar to 2 galaxies using early observations from the MOSFIRE Deep Evolution Field survey. Our sample consists of 224 star-forming galaxies with z(spec) = 1.36-2.59 and high signal-to-noise ratio measurements of H alpha and H beta obtained with Keck/MOSFIRE. We construct composite spectral energy distributions (SEDs) of galaxies in bins of Balmer decrement to measure the attenuation curve. We find a curve that is similar to the SMC extinction curve at lambda greater than or similar to 2500 angstrom. At shorter wavelengths, the shape is identical to that of the Calzetti et al. relation, but with a lower normalization. Hence, the new attenuation curve results in star formation rates (SFRs) that are approximate to 20% lower, and stellar masses that are Delta log(M* M-circle dot)similar or equal to 0.16dex lower, than those obtained with the Calzetti relation. We find that the difference in the total attenuation of the ionized gas and stellar continuum correlates strongly with SFR, such that for dust-corrected SFRs. 20M(circle dot) yr(-1), assuming a Chabrier initial mass function, the nebular emission lines suffer an increasing degree of obscuration relative to the continuum. A simple model that can account for these trends is one in which the UV through optical stellar continuum is dominated by a population of less-reddened stars, while the nebular line and bolometric luminosities become increasingly dominated by dustier stellar populations for galaxies with large SFRs, as a result of the increased dust enrichment that accompanies such galaxies. Consequently, UV-and SED-based SFRs may underestimate the total SFR at even modest levels of similar to 20M(circle dot) yr(-1).