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

Variations in the dust emissivity index, |$\beta$|⁠ , 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 |$\beta$| and dust temperature for a sample of 109 dusty star-forming galaxies (DSFGs) over the range, |$2 \ \lt\ z \ \lt\ 6$|⁠. We compare the results obtained with both an optically thin model and a general opacity model, finding that our estimates of |$\beta$| are similar between the models but our estimates of dust temperature are not. We find no evidence of a change in |$\beta$| with redshift, with a median value of |$\beta = 1.96$| for the optically thin model with a confidence interval (16–84&#160;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 |$\beta$| in 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, |$T_{\textrm {dust}}$|⁠ , with redshift. After allowing for the effects of correlated measurement errors, we find an inverse correlation between |$\beta$| and |$T_{\textrm {dust}}$| in DSFGs, for which there is also evidence in low-redshift galaxies. [ABSTRACT FROM AUTHOR]