Radiative transfer of ionizing radiation through gas and dust: grain charging in star forming regions

TL;DR

This paper introduces a new method for simulating grain charging in the interstellar medium within radiative transfer models, revealing complex charge distributions influenced by radiation and dust properties in star forming regions.

Contribution

A novel implementation of grain charging in the CRASH radiative transfer code, enabling detailed simulations of dust charge dynamics in star forming environments.

Findings

~13% of dust mass becomes negatively charged

Charge distribution varies with radiation exposure and line of sight

Grain properties significantly influence charge distribution

Abstract

The presence of charged dust grains is known to have a profound impact on the physical evolution of the multiphase interstellar medium (ISM). Despite its importance, this process is still poorly explored in numerical simulations due to its complex physics and the tight dependence on the environment. Here we introduce a novel implementation of grain charging in the cosmological radiative transfer code CRASH. We first benchmark the code predictions on a series of idealized dusty HII regions created by a single star, in order to assess the impact of grain properties on the resulting spatial distribution of charges. Second, we perform a realistic radiative transfer simulation of a star forming region extracted from a dusty galaxy evolving in the Epoch of Reionization. We find that $\sim 13$ % of the total dust mass gets negatively charged, mainly silicate and graphite grains of radius micron. A complex spatial distribution of grain charges is also found, primarily depending on the exposure to stellar radiation and strongly varying along different lines of sight, as a result of radiative transfer effects. We finally assess the impact of grain properties (both chemical composition and size) on the resulting charge distribution. The new implementation described here will open up a wide range of possible studies investigating the physical evolution of the dusty ISM, nowadays accessible to observations of high and low redshift galaxies.