The Dust Attenuation of Star-forming Galaxies at $z\sim 3$ and Beyond: New Insights from ALMA Observations

Abstract

We present results on the dust attenuation of galaxies at redshift $\sim 3-6$ by studying the relationship between the UV spectral slope (${\hat{I}}_{\mathrm{UV}}^2$) and the infrared excess (IRX; $L_{\mathrm{IR}}$/$L_{\mathrm{UV}}$) using ALMA far-infrared continuum observations. Our study is based on a sample of 67 massive, star-forming galaxies with a median mass of $M_{\ast }\sim 10^{10.7}{M}_{\odot }$ spanning a redshift range $z=2.6-3.7$ (median $z=3.2$) that were observed with ALMA at $\hat{I}{»}_{rest}=300\hat{\mathrm{I}}¼\mathrm{m}$. Both the individual ALMA detections (41 sources) and stacks including all galaxies show the IRX-${\hat{I}}_{\mathrm{UV}}^2$ relationship at $z\sim 3$ is mostly consistent with that of local starburst galaxies on average. However, we find evidence for a large dispersion around the mean relationship by up to $\pm 0.5$ dex. Nevertheless, the locally calibrated dust correction factors based on the IRX-${\hat{I}}_{\mathrm{UV}}^2$ relation are on average applicable to main-sequence $z\sim 3$ galaxies. This does not appear to be the case at even higher redshifts, however. Using public ALMA observations of $z\sim 4-6$ galaxies we find evidence for a significant evolution in the IRX-${\hat{I}}_{\mathrm{UV}}^2$ and the IRX-$M_{\ast }$ relations beyond $z\sim 3$ toward lower IRX values. We discuss several caveats that could affect these results, including the assumed dust temperature. ALMA observations of larger $z>3$ galaxy samples will be required to confirm this intriguing redshift evolution.

8 pages, 4 figures, submitted to MNRAS; v2 - Small changes to text