A photon dominated region code comparison study

By M. Röllig, N. Abel, T. Bell, F. Bensch, J. Black, G. Ferland, B. Jonkheid, I. Kamp, M. Kaufman, Jacques Le Bourlot and 14 more. 2007

234 citations recorded by the source corpus.

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 = 10 3 , 10 5.5 cm −3 and far ultraviolet intensities χ = 10, 10 5 in units of the Draine field (FUV: 6 < h ν< 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.

Subfields: Astronomy and Astrophysics, Atmospheric Science, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/dc1b8061ad15b9d3deb0bcb2b6c568a9c024f259

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Citations in the corpus

CO Isotopologues in the Perseus Molecular Cloud Complex: the X-factor and Regional Variations (2008, methodology): “…of the regions, we use the Meudon PDR code (Le Petit et al. 2006).3 This code includes most physical effects by explicit calculation; in particular it calculates the 12CO shielding, unlike the majority of other codes available (e.g., Röllig et al. 2007), where fitting formulae are used instead.”
A comparison of chemistry and dust cloud formation in ultracool dwarf model atmospheres (2008, background): “Comparative studies have been carried out for simulations of radiative transfer (Pascucci et al. 2004; Iliev et al. 2006), white dwarfs (Barstow et al. 2001) or photon-dominated region (Röllig et al. 2007).”
ROTATIONAL QUENCHING OF CO DUE TO H2 COLLISIONS (2010, background): “In recent years, various codes that model the physics and chemistry of PDRs have been developed with an emphasis on the excitation mechanisms of both H2 and CO (van Dishoeck & Black 1988; Warin et al. 1996; Le Petit et al. 2006; Shaw et al. 2005; Röllig et al. 2007).”
Ultraviolet Survey of CO and H2 in Diffuse Molecular Clouds: The Reflection of Two Photochemistry Regimes in Abundance Relationships (2008, methodology): “The temperature is computed from energy conservation consisting of a host of microphysical processes (Ferland et al. 1998; Abel et al. 2005; Röllig et al. 2007).”
Dynamics of Protoplanetary Disks (2010, background): “Accounting accurately for these effects remains challenging, with independent codes returning somewhat different predictions for the gas temperature even when the same physical assumptions are adopted (Röllig et al. 2007).”
On the relationship between molecular hydrogen and carbon monoxide abundances in molecular clouds (2010, background): “For these reasons, we would expect the CO/H2 ratio to vary through a cloud, and this expectation is confirmed by detailed models of slab-like or spherical clouds (e.g. Röllig et al. 2007).”
THE PdBI ARCSECOND WHIRLPOOL SURVEY (PAWS). I. A CLOUD-SCALE/MULTI-WAVELENGTH VIEW OF THE INTERSTELLAR MEDIUM IN A GRAND-DESIGN SPIRAL GALAXY (2013, methodology): “A comparison of contemporary PDR codes summarizing the main characteristics deemed important is presented by Röllig et al. (2007).”
Reaction Networks for Interstellar Chemical Modelling: Improvements and Challenges (2010, background): “Complex albeit steady-state models have been constructed for so-called Photon-dominated regions (PDR’s), which are heterogeneous sources located near stars (Hollenbach and Tielens 1997; Röllig et al. 2007).”
Radiation thermo-chemical models of protoplanetary disks I. Hydrostatic disk structure and inner rim (2009, background): “Röllig et al. (2007) relateχ = 1 to a “unit Draine field” and we will follow this idea in ProDiMo.”
Cool Gas in High-Redshift Galaxies (2013, methodology): “The gas temperatures calculated in PDR/XDR models are still quite uncertain and depend on the code used, especially in the high–denisty, high–UV case (e.g., Röllig et al. 2007).”
The warm gas atmosphere of the HD 100546 disk seen by Herschel - Evidence of a gas-rich, carbon-poor atmosphere? (2012, methodology): “A small chemical network from the PDR comparison study by Röllig et al. (2007) is used for this test.”
The photodissociation and chemistry of CO isotopologues: applications to interstellar clouds and circumstellar disks (2009, methodology): “We adopt the network from a recent PDR benchmark study (Röllig et al. 2007), which includes only 31 species consisting of H, He, C and O.”
Chemistry in Disks. IV. Benchmarking gas-grain chemical models with surface reactions (2010, methodology): “We do not take the Lyα radiation into account as it requires sophisticated modeling of the radiation transport – a full-scale benchmarking study by itself (e.g., Pascucci et al., 2004; Röllig et al., 2007).”
Survival of molecular gas in cavities of transition disks - I. CO (2013, methodology): “A comparison of PDR models run for a density/FUV intensity combination corresponding to the outer disk has revealed a scatter of a factor of a few in gas temperature (Röllig et al. 2007).”
A NEW NETWORK FOR HIGHER-TEMPERATURE GAS-PHASE CHEMISTRY. I. A PRELIMINARY STUDY OF ACCRETION DISKS IN ACTIVE GALACTIC NUCLEI (2010, methodology): “Indeed, the modeling of PDRs remains a major topic of study (for model comparison, see Röllig et al. 2007), while XDRs are also of high interest (Maloney et al. 1996; Meijerink & Spaans 2005; Stäuber et al. 2005; Meijerink et al. 2007).”