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

Evolution of dust temperature of galaxies through cosmic time as seen by Herschel

We study the dust properties of galaxies in the redshift range 0.1 ≲z≲ 2.8 observed by the Herschel Space Observatory in the field of the Great Observatories Origins Deep Survey-North as part of the PACS Extragalactic Probe (PEP) and Herschel Multi-tiered Extragalactic Survey (HerMES) key programmes. Infrared (IR) luminosity (LIR) and dust temperature (Tdust) of galaxies are derived from the spectral energy distribution fit of the far-IR (FIR) flux densities obtained with the PACS and SPIRE instruments onboard Herschel. As a reference sample, we also obtain IR luminosities and dust temperatures of local galaxies at z < 0.1 using AKARI and IRAS data in the field of the Sloan Digital Sky Survey. We compare the LIR–Tdust relation between the two samples and find that the median Tdust of Herschel-selected galaxies at z≳ 0.5 with LIR≳ 5 × 1010 L⊙ appears to be 2–5 K colder than that of AKARI-selected local galaxies with similar luminosities, and the dispersion in Tdust for high-z galaxies increases with LIR due to the existence of cold galaxies that are not seen among local galaxies. We show that this large dispersion of the LIR−Tdust relation can bridge the gap between local star-forming galaxies and high-z submillimetre galaxies (SMGs). We also find that three SMGs with very low Tdust (≲20 K) covered in this study have close neighbouring sources with similar 24-μm brightness, which could lead to an overestimation of FIR/(sub)millimetre fluxes of the SMGs