A photon dominated region code comparison study
Journal article, 2007
Aims.We present a comparison between independent computer codes, modeling the physics and chemistry of interstellar photon dominated regions (PDRs). Our goal was to understand the mutual differences in the PDR codes and their effects on the physical and chemical structure of the model clouds, and to converge the output of different codes to a common solution.
Methods. A number of benchmark models have been created, covering low and high gas densities n = 103,105.5 cm-3 and far ultraviolet intensities $\chi$ = 10, 105 in units of the Draine field (FUV: 6 < $h\,\nu$ < 13.6 eV). The benchmark models were computed in two ways: one set assuming constant temperatures, thus testing the consistency of the chemical network and photo-processes, and a second set determining the temperature self consistently by solving the thermal balance, thus testing the modeling of the heating and cooling mechanisms accounting for the detailed energy balance throughout the clouds.
Results.We investigated the impact of PDR geometry and agreed on the comparison of results from spherical and plane-parallel PDR models. We identified a number of key processes governing the chemical network which have been treated differently in the various codes such as the effect of PAHs on the electron density or the temperature dependence of the dissociation of CO by cosmic ray induced secondary photons, and defined a proper common treatment. We established a comprehensive set of reference models for ongoing and future PDR model bench-marking and were able to increase the agreement in model predictions for all benchmark models significantly. Nevertheless, the remaining spread in the computed observables such as the atomic fine-structure line intensities serves as a warning that there is still a considerable uncertainty when interpreting astronomical data with our models.
radiative transfer
ISM: clouds
ISM: general
astrochemistry
methods: numerical
ISM: abundances
Author
M. Röllig
University of Cologne
N. P. Abel
University of Kentucky
T. A. Bell
University College London (UCL)
F. Bensch
University of Bonn
John H Black
Chalmers, Department of Radio and Space Science
G. J. Ferland
University of Kentucky
B. Jonkheid
Leiden University
I. Kamp
Space Telescope Science Institute (STScI)
M. J. Kaufman
San Jose State University
J. Le Bourlot
Centre national de la recherche scientifique (CNRS)
Franck Le Petit
Chalmers, Department of Radio and Space Science
R. Meijerink
Leiden University
O. Morata
V. Ossenkopf
University of Cologne
E. Roueff
Centre national de la recherche scientifique (CNRS)
G. Shaw
University of Kentucky
M. Spaans
Kapteyn Astronomical Institute
A. Sternberg
Tel Aviv University
J. Stutzki
University of Cologne
W. F. Thi
University of Edinburgh
E. F. van Dishoeck
Leiden University
P. A. M. van Hoof
Royal Observatory of Belgium
S. Viti
University College London (UCL)
M.G. Wolfire
University of Maryland
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 467 No. 1 (May III 2007) 187-206Subject Categories
Astronomy, Astrophysics and Cosmology
DOI
10.1051/0004-6361:20065918