Little evolution of dust emissivity in bright infrared galaxies from 2 < z < 6

Abstract

Variations in the dust emissivity index, β, within and between galaxies, are evidence that the chemistry and physics of dust must vary on large scales, although the nature of the physical and/or chemical variations is still unknown. In this paper, we estimate values of βand dust temperature for a sample of 109 dusty star-forming galaxies (DSFGs) over the range, 2 < z < 6. We compare the results obtained with both an optically thin model and a general opacity model, finding that our estimates of βare similar between the models but our estimates of dust temperature are not. We find no evidence of a change in βwith redshift, with a median value of β= 1 . 96 for the optically thin model with a confidence interval (16-84 per cent) of 1.67 to 2.35 for the population. Using simulations, we estimate the measurement errors from our procedure and show that the variation of βin the population results from intrinsic variations in the properties of the dust in DSFGs. At a fixed far-infrared luminosity, we find no evidence for a change in dust temperature, Tdust, with redshift. After allowing for the effects of correlated measurement errors, we find an inverse correlation between βand Tdust in DSFGs, for which there is also evidence in low-redshift galaxies.