The HDUV Survey: A Revised Assessment of the Relationship between UV Slope and Dust Attenuation for High-redshift Galaxies

We use a newly assembled sample of 3545 star-forming galaxies with secure spectroscopic, grism, and photometric redshifts at z = 1.5-2.5 to constrain the relationship between UV slope (beta) and dust attenuation (L-IR/L-UV IRX). Our sample significantly extends the range of L-UV and beta probed in previous UV-selected samples, including those as faint as M-1600 = -17.4 (similar or equal to 0.05L(UV)*) and -2.6 less than or similar to beta less than or similar to 0.0. IRX is measured using stacks of deep Herschel data, and the results are compared with predictions of the IRX-beta relation for different assumptions of the stellar population model and obscuration curve. We find that z = 1.5-2.5 galaxies have an IRX-beta relation that is consistent with the predictions for an SMC curve if we invoke subsolar-metallicity models currently favored for high-redshift galaxies, while the commonly assumed starburst curve overpredicts the IRX at a given beta by a factor of greater than or similar to 3. IRX is roughly constant with L-UV for L-UV greater than or similar to 3 x 10(9) L-circle dot. Thus, the commonly observed trend of fainter galaxies having bluer beta may simply reflect bluer intrinsic slopes for such galaxies, rather than lower obscurations. The IRX-beta relation for young/low-mass galaxies at z greater than or similar to 2 implies a dust curve that is steeper than the SMC. The lower attenuations and higher ionizing photon output for low-metallicity stellar populations point to Lyman continuum production efficiencies, xi(ion), that may be elevated by a factor of approximate to 2 relative to the canonical value for L* galaxies, aiding in their ability to keep the universe ionized at z similar to 2.