Abstract
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 H ii regions created by a single star, in order to assess the impact of grain properties on the resulting spatial distribution of charges. Secondly, 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 ∼13 per cent of the total dust mass gets negatively charged, mainly silicate and graphite grains of radius 10−3 $\mu$m. 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.
Highlights
Recent high redshift observations (e.g. Knudsen et al 2017; Tamura et al 2019; Hashimoto et al 2019; Bakx et al 2020) show that dusty galaxies are present in the young Universe, well before the end of the epoch of reionization (EoR), at z 6 (Bouwens et al 2021)
Detections at these redshifts are biased towards bright objects, they indicate that the interstellar medium (ISM) of many young galaxies is chemically evolved and could even contain a significant amount of cosmic dust obscuring these objects in certain electromagnetic bands (Fudamoto et al 2021)
The grain charges obtained in a more realistic case are discussed in § 4.3, where dust, gas and stellar source distributions are motivated by a hydrodynamical simulation and the spectrum of each stellar population is modelled using BPASS (Stanway & Eldridge 2018)
Summary
Recent high redshift observations (e.g. Knudsen et al 2017; Tamura et al 2019; Hashimoto et al 2019; Bakx et al 2020) show that dusty galaxies are present in the young Universe, well before the end of the epoch of reionization (EoR), at z 6 (Bouwens et al 2021). Mancini et al 2015; McKinnon et al 2017; Popping et al 2017; Gioannini et al 2017; Aoyama et al 2018; Graziani et al 2020) that some form of grain growth is necessary to reproduce the total mass of dust in galaxies across cosmic timescales, while its efficiency remains controversial (Priestley et al 2021) When studying this process, grain charge has to be considered, as the arrival rate of candidate ions for accretion (e.g. Si+) can be significantly modified by a non-zero charge (e.g. Zhukovska et al 2018). Despite the relevance of the charging process, to our knowledge, no available galaxy formation model explicitly accounts for it, since the physics regulating the process of charging depends on a number of variables at the ISM scale, poorly constrained or unresolved in numerical simulations: e.g. the free electron temperature, the plasma ionization status and chemical composition, as well as the presence of a UV and/or X-/cosmic ray flux.
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