An empirical study of dust properties at the earliest epochs

Abstract

We present an empirical analysis of the properties of dust-continuum emission in a sample of 17 galaxies in the early Universe (4 < z < 8) with well-sampled far-infrared spectral energy distributions (SEDs) compiled from the literature. We place our results into context by self-consistently comparing to samples of nearby star-forming galaxies, luminous infrared galaxies (LIRGs), and quasars. With the exception of two sources, we find no significant evolution in the dust emissivity index across cosmic time, measuring a consistent value of βIR = 1.8 ± 0.3 at z > 4, suggesting that the effective dust properties do not change dramatically for most galaxies. Despite having comparable stellar masses, we find the high-redshift galaxies to be similar to, or even more extreme than, LIRGs in the Herschel (U)LIRG Survey, where (U)LIRG refers to (ultra-)LIRG, sample in terms of dust temperature () and infrared (IR) luminosity (). We find that the dust temperature evolves mildly towards high redshift, though the LIRGs and quasars exhibit elevated temperatures indicating a more efficient and/or additional heating mechanism. Where available, we compare stellar mass estimates to our inferred dust masses, whose degeneracy with dust temperature can only be mitigated with a well-constrained SED. In merely half of the cases, the dust yield may be explained by supernovae alone, with four sources () significantly exceeding a highly optimistic yield where Mdust ≈ 0.01M∗. We discuss possible explanations for this apparent inconsistency and potential observational biases in the measurements of the dust properties of high-redshift galaxies, including in the current IR-bright sample.