Journal Article

3D-PDR: a new three-dimensional astrochemistry code for treating photodissociation regions

T. G. Bisbas, T. A. Bell, S. Viti, J. Yates and M. J. Barlow

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 427, issue 3, pages 2100-2118
Published in print December 2012 | ISSN: 0035-8711
Published online December 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.22077.x
3D-PDR: a new three-dimensional astrochemistry code for treating photodissociation regions

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Abstract

Photodissociation regions (PDRs) define the transition zone between an ionized and a dark molecular region. They consist of neutral gas which interacts with far-ultraviolet radiation and are characterized by strong infrared line emission. Various numerical codes treating one-dimensional PDRs have been developed in the past, simulating the complexity of chemical reactions occurring and providing a better understanding of the structure of a PDR. In this paper we present the three-dimensional code, 3d-pdr, which can treat PDRs of arbitrary density distribution. The code solves the chemistry and the thermal balance self-consistently within a given three-dimensional cloud. It calculates the total heating and cooling functions at any point in a given PDR by adopting an escape probability method. It uses a healpix-based ray tracing scheme to evaluate the attenuation of the far-ultraviolet radiation in the PDR and the propagation of the far-infrared/submm line emission out of the PDR. We present benchmarking results and apply 3d-pdr to (i) a uniform-density spherical cloud interacting with a plane-parallel external radiation field, (ii) a uniform-density spherical cloud interacting with a two-component external radiation field and (iii) a cometary globule interacting with a plane-parallel external radiation field. We find that the code is able to reproduce the benchmarking results of various other one-dimensional numerical codes treating PDRs. We also find that the accurate treatment of the radiation field in the fully three-dimensional treatment of PDRs can in some cases leads to different results when compared to a standard one-dimensional treatment.

Keywords: astrochemistry; radiative transfer; methods: numerical; ISM: abundances; photodissociation region (PDR)

Journal Article.  12306 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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