Dust extinction and emission in a clumpy galactic disk

Abstract

Aims. I present the Monte Carlo radiative transfer code TRADING (Transfer of RAdiation through Dust In Galaxies). The code selfconsistently computes 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 conditions, 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 is 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; 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.

FitSKIRT: genetic algorithms to automatically fit dusty galaxies with a Monte Carlo radiative transfer code

“…Kylafis & Bahcall 1987;Xilouris et al 1997Xilouris et al , 1999Bianchi 2007Bianchi , 2008Baes et al 2010;Popescu et al 2011;MacLachlan et al 2011;Holwerda et al 2012). The system consists of a stellar disc, a stellar bulge and a dust disc.…”

“…They used an approximation of a de Vaucouleurs model to fit the bulge and excluded the central 200 pc from the fit. The modelling of NGC 4013 by Bianchi (2007) on the other hand was based on the Monte Carlo code TRADING (Bianchi et al 1996(Bianchi et al , 2000Bianchi 2008). For the actual fitting, he used a combination of the Levenberg-Marquardt algorithm (applied to model without scattering) and the amoeba downhill simplex algorithm.…”

“…Fortunately, several powerful 3D radiative transfer A&A 550, A74 (2013) codes with these characteristics have recently been developed (e.g. Gordon et al 2001;Baes et al 2003Jonsson 2006;Bianchi 2008;Robitaille 2011).…”

Detection of a large amount of diffuse extraplanar dust in NGC 891

“…The SED in FIR/submm requires at least a dust mass twice as large as estimated from the radiative transfer model of optical/NIR images (Popescu et al 2000;Bianchi 2008). To resolve this discrepancy, an extra dust mass in the form of a secondary thin (even thinner than the thin disk found from optical/NIR observations) disk + clumpy dust clouds associated with molecular clouds that was supposed to be hidden in optical images was introduced (Popescu et al 2000;Tuffs et al 2004;Bianchi 2008;Popescu et al 2011). However, the model produces a dust lane in K-band that is much stronger than that observed (Dasyara et al 2005;Bianchi 2008).…”

Composite biasing in Monte Carlo radiative transfer

“…Actually, no more than 10 lines of code were altered on a total of more than 50,000 lines in the current version of SKIRT. While all test performed in this paper were run with SKIRT, composite path length stretching was also implemented in DIRTY, TRADING (Bianchi 2008), and CRT (Lunttila & Juvela 2012).…”