Dust Attenuation of Star-Forming Galaxies at z~3 and Beyond New Insights from ALMA Observations (arXiv:1705.01559)

<p>We present results on the dust attenuation of galaxies at redshift ~3-6 by studying the relationship between the UV spectral slope (ß_UV) and the infrared excess (IRX; L_IR/L_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_* ~10^10.7 M_$\odot$ spanning a redshift range z=2.6-3.7 (median z=3.2) that were observed with ALMA band-6. Both the individual ALMA detections (41 sources) and stacks including all galaxies show the IRX-ß_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 $\pm$0.5 dex. Nevertheless, the locally calibrated dust correction factors based on the IRX-ß_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-ß_UV 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.</p

A direct calibration of thtae IRX-beta relation in Lyman-break Galaxies at z=3-5

We use a sample of 4209 Lyman-break galaxies (LBGs) at z 3, 4, and 5 in the UKIRT Infrared Deep Sky Survey Ultra Deep Survey field to investigate the relationship between the observed slope of the stellar continuum emission in the ultraviolet, β, and the thermal dust emission, as quantified via the so-called ‘infrared excess’ (IRX ≡ LIR/LUV). Through a stacking analysis, we directly measure the 850-μm flux density of LBGs in our deep (0.9 mJy) James Clerk Maxwell Telescope SCUBA-2 850-μm map as well as deep public Herschel/SPIRE 250-, 350-, and 500-μm imaging. We establish functional forms for the IRX–β relation to z ∼ 5, confirming that there is no significant redshift evolution of the relation, and that the resulting average IRX–β curve is consistent with a Calzetti-like attenuation law. Comparing our results with recent works in the literature, we confirm that discrepancies in the slope of the IRX–β relation are driven by biases in the methodology used to determine the ultraviolet slopes. Consistent results are found when IRX–β is evaluated by stacking in bins of stellar mass, and we argue that the near-linear IRX–M relationship is a better proxy for correcting observed ultraviolet luminosities to total star formation rates, provided an accurate handle on M and also gives clues as to the physical driver of the role of dust-obscured star formation in high-redshift galaxie