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

## TL;DR

This study uses a large, high-redshift galaxy sample to refine the UV slope and dust attenuation relationship, supporting an SMC-like dust curve and highlighting mass and metallicity effects on dust properties and ionizing photon output.

## Contribution

It provides new empirical constraints on the IRX-beta relation at z=1.5-2.5, favoring SMC-like extinction curves and linking stellar mass and metallicity to dust attenuation and ionization efficiency.

## Key findings

- IRX-beta relation consistent with SMC extinction curve at high redshift.
- High-mass galaxies exhibit significantly higher IRX than low-mass galaxies.
- Low-metallicity, young galaxies have steeper dust curves and higher ionizing photon efficiencies.

## Abstract

We use a newly assembled large sample of 3,545 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 benefits from the combination of deep Hubble WFC3/UVIS photometry from the Hubble Deep UV (HDUV) Legacy survey and existing photometric data compiled in the 3D-HST survey, and extends the range of UV luminosity and beta probed in previous UV-selected samples. IRX is measured using stacks of deep Herschel/PACS 100 and 160 micron 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 extinction curve if we invoke sub-solar metallicity models that are currently favored for high-redshift galaxies, while the commonly assumed starburst attenuation curve over-predicts the IRX at a given beta by a factor of ~3. The IRX of high-mass (M*>10^9.75 Msun) galaxies is a factor of >4 larger than that of low-mass galaxies, lending support for the use of stellar mass as a proxy for attenuation. The commonly observed trend of fainter galaxies having bluer beta may simply reflect bluer intrinsic UV slopes for such galaxies, rather than lower obscurations. The IRX-beta for young/low-mass galaxies implies a dust curve that is steeper than the SMC, suggesting a lower attenuation at a given beta relative to older/more massive galaxies. The lower attenuations and higher ionizing photon output implied by low metallicity stellar population models point to Lyman continuum production efficiencies, xi_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. [Abridged]