The dust emissivity index beta in infrared-bright galaxies at 1.5 < z < 4.2

TL;DR

This study measures the dust emissivity index beta in 21 high-redshift infrared-bright galaxies using ALMA data, finding higher beta values than previously reported, which impacts dust emission modeling.

Contribution

It provides robust beta measurements at high redshift using ALMA data, revealing higher values and no redshift dependence, influencing dust mass and optical depth estimates.

Findings

Mean beta of 2.2 with a standard deviation of 0.6

No systematic variation of beta with redshift

Higher beta values significantly affect dust emission models

Abstract

We have measured the dust emissivity index beta for 21 infrared-bright sources (including several gravitationally lensed galaxies) at 1.5 < z < 4.2 using Atacama Large Millimeter/submillimeter Array (ALMA) 101-199 GHz data sampling the Rayleigh-Jeans side of the SED. These data are largely insensitive to temperature variations and therefore should provide robust measurements of beta. We obtain a mean beta of 2.2 with a standard deviation of 0.6 that is at the high end of the range of values that had previously been measured in many galactic and extragalactic sources. We find no systematic variation in beta versus redshift. We also demonstrate with a subset of our sources that these higher beta values have significant implications for modelling dust emission and in particular for calculating dust masses or the wavelength at which dust becomes optically thick.