The dust attenuation of star-forming galaxies at z ~ 3 and beyond: New insights from ALMA observations

We present results on the dust attenuation of galaxies at redshift ~3-6 by studying the relationship between the UV spectral slope (β_UV) and the infrared excess (IRX; LIR/LUV) using Atacama Large Millimeter/submillimeter Array (ALMA) far-infrared continuum observations. Our study is based on a sample of 67 massive, star-forming galaxies with a median mass of M* ~ 10¹⁰.7 M_⊙ spanning a redshift range z = 2.6-3.7 (median z = 3.2) that were observed with ALMA at λ_rest = 300 μm. Both the individual ALMA detections (41 sources) and stacks including all galaxies show the IRX-β_UV relationship at z ~ 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 ±0.5 dex. Nevertheless, the locally calibrated dust correction factors based on the IRX-β_UV relation are on average applicable to main-sequence z ~ 3 galaxies. This does not appear to be the case at even higher redshifts, however. Using public ALMA observations of z ~ 4-6 galaxies we find evidence for a significant evolution in the IRX-β_UV and the IRX-M* relations beyond z ~ 3 towards lower IRX values. We discuss several caveats that could affect these results, including the assumed dust temperature. ALMA observations of larger z > 3 galaxy sample spanning a wide range of physical parameters (e.g. lower stellar mass) will be important to investigate this intriguing redshift evolution further.