Dust Extinction and Emission in a Clumpy Galactic Disk. An Application of the Radiative Transfer Code TRADING

TL;DR

This paper introduces the TRADING Monte Carlo radiative transfer code for modeling dust extinction and emission in clumpy galactic disks, successfully reproducing the spectral energy distribution of galaxy NGC 891.

Contribution

The paper presents a new radiative transfer code that self-consistently models dust extinction and emission in complex, clumpy galactic environments, including stochastic heating effects.

Findings

The model accurately reproduces NGC 891's SED from UV to submm/mm.

Approximately 35% of bolometric radiation is absorbed and re-emitted by dust.

Dust emission from clouds is significantly influenced by diffuse radiation absorption.

Abstract

AIMS: I present the Monte Carlo radiative transfer code TRADING (Transfer of RAdiation through Dust In Galaxies). The code computes self-consistently the extinction of radiation in a dusty medium (including absorption and scattering) and the dust emission. METHODS: A binary-tree adaptive grid is used for the description of the dust distribution. Dust radiation is computed at thermal equilibrium or under stochastic heating condition, for a distribution of grains of different radii and materials. The code is applied to the case of a clumpy galactic disk, including both diffuse dust and a distribution of spherical clouds modelled on the GMCs of local galaxies. Diffuse and localised sources of starlight are used, with independent spectra. RESULTS: A model is provided for the edge-on galaxy NGC 891. The SED of the galaxy from the UV to the submm/mm range can be well reproduced by: a bulge/disk configuration of old stars together with an extended dust disk, as suggested by the analysis of optical/near-infrared images; a clumpy dust distribution of the same mass as the diffuse dust disk, together with a UV emitting component, half of which in the form of a diffuse disk and half in sources embedded in clouds. In total, it is found that about 35% of the bolometric radiation is absorbed (and emitted) by dust; and that absorption of starlight from the old population contributes to about 60% of the dust emission. A significant component of the dust emission from clouds is due to absorption of diffuse radiation. Radial profiles of dust emission in a clumpy disk are almost independent of the wavelength, with the exception of the wavelength range on the Wien side of the thermal equilibrium peak.