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

Reddy, Naveen A, Oesch, Pascal A, Bouwens, Rychard, Montes, Mireia, Illingworth, Garth D, Steidel, Charles C, van Dokkum, Pieter G, Atek, Hakim, Carollo, Marcella C, Cibinel, Anna, Holden, Brad, Labbé, Ivo, Magee, Dan, Morselli, Laura, Nelson, Erica J and Wilkins, Steve (2018) The HDUV Survey: A Revised Assessment of the Relationship between UV Slope and Dust Attenuation for High-redshift Galaxies. The Astrophysical Journal, 853 (56). pp. 1-20. ISSN 1538-4357

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 (β) and dust attenuation (L IR/L UV ≡ IRX). Our sample significantly extends the range of L UV and β probed in previous UV-selected samples, including those as faint as M 1600 = −17.4 ($\simeq 0.05{L}_{\mathrm{UV}}^{* }$) and −2.6 lesssim β lesssim 0.0. IRX is measured using stacks of deep Herschel data, and the results are compared with predictions of the IRX−β relation for different assumptions of the stellar population model and obscuration curve. We find that z = 1.5–2.5 galaxies have an IRX−β 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 β by a factor of gsim3. IRX is roughly constant with L UV for L UV gsim 3 × 109 L ⊙. Thus, the commonly observed trend of fainter galaxies having bluer β may simply reflect bluer intrinsic slopes for such galaxies, rather than lower obscurations. The IRX−β relation for young/low-mass galaxies at z gsim 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, ξ ion, that may be elevated by a factor of ≈2 relative to the canonical value for L* galaxies, aiding in their ability to keep the universe ionized at z ~ 2.