# Parameterizing the interstellar dust temperature

## TL;DR

This paper derives a simple parametric formula for interstellar dust temperature based on visual extinction and grain composition, validated against observations, and explores the impact of ices on dust heating.

## Contribution

It provides an easy-to-use analytical expression for dust temperature as a function of extinction and grain type, improving modeling accuracy in astrophysical simulations.

## Key findings

- Mixed carbonaceous-silicate dust matches observations best.
- Ice formation increases dust temperature by up to 15% at high extinction.
- The proposed formula accurately reproduces observed dust temperatures.

## Abstract

The temperature of interstellar dust particles is of great importance to astronomers. It plays a crucial role in the thermodynamics of interstellar clouds, because of the gas-dust collisional coupling. It is also a key parameter in astrochemical studies that governs the rate at which molecules form on dust. In 3D (magneto)hydrodynamic simulations often a simple expression for the dust temperature is adopted, because of computational constraints, while astrochemical modelers tend to keep the dust temperature constant over a large range of parameter space. Our aim is to provide an easy-to-use parametric expression for the dust temperature as a function of visual extinction ($A_{\rm V}$) and to shed light on the critical dependencies of the dust temperature on the grain composition. We obtain an expression for the dust temperature by semi-analytically solving the dust thermal balance for different types of grains and compare to a collection of recent observational measurements. We also explore the effect of ices on the dust temperature. Our results show that a mixed carbonaceous-silicate type dust with a high carbon volume fraction matches the observations best. We find that ice formation allows the dust to be warmer by up to 15% at high optical depths ($A_{\rm V}> 20$ mag) in the interstellar medium. Our parametric expression for the dust temperature is presented as $T_{\rm d} = \left[ 11 + 5.7\times \tanh\bigl( 0.61 - \log_{10}(A_{\rm V})\bigr) \right] \, \chi_{\rm uv}^{1/5.9}$, where $\chi_{\rm uv}$ is in units of the Draine (1978) UV field