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

摘要

We present results on the dust attenuation of galaxies at redshift ∼3−6 by studying the relationship between the UV spectral slope (βUV) and the infrared excess (IRX; LIR/LUV) 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∗∼10^10.7M⊙ spanning a redshift range z=2.6−3.7 (median z=3.2) that were observed with ALMA at λrest=300μm. Both the individual ALMA detections (41 sources) and stacks including all galaxies show the IRX-βUV 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-βUV 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-βUV and the IRX-M∗ relations beyond z∼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.