Inverse temperature dependence of the dust submillimeter spectral index

TL;DR

This study compiles PRONAOS data revealing an inverse relationship between dust spectral index and temperature, with variations explained by grain size, composition, or quantum effects across diverse astrophysical environments.

Contribution

It provides the first comprehensive analysis of the temperature dependence of dust spectral index using PRONAOS data across multiple environments.

Findings

Spectral index varies from 0.8 to 2.4 across 12-80 K.

Spectral indices are higher in cold regions and lower in warm regions.

The variation follows a hyperbolic function of temperature.

Abstract

We present here a compilation of PRONAOS-based results concerning the temperature dependence of the dust submillimeter spectral index, including data from Galactic cirrus, star-forming regions and a circumstellar envelope. We observe large variations of the spectral index (from 0.8 to 2.4) in a wide range of temperatures (12 to 80 K). These spectral index variations follow a hyperbolic-shaped function of the temperature, large spectral indices (1.5-2.4) being observed in cold regions (12-20 K) while small indices (0.8-1.6) are observed in warm regions (35-80 K). Three interpretations are proposed: one is that the grain sizes change in warm and rather dense environments, another is that the chemical composition of the grains is not the same in different environments, a third one is that there is an intrinsic dependence of the dust spectral index on the temperature due to quantum processes.