Universität zu Köln

Andree-Labsch, S., Ossenkopf-Okada, V. and Roellig, M. (2017). Modelling clumpy photon-dominated regions in 3D Understanding the Orion Bar stratification. Astron. Astrophys., 598. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

Full text not available from this repository.

Abstract

Context. Models of photon-dominated regions (PDRs) still fail to fully reproduce some of the observed properties. In particular they do not reproduce the combination of the intensities of different PDR cooling lines together with the chemical stratification, as observed for example for the Orion Bar PDR. Aims. We aim to construct a numerical PDR model, KOSMA-tau 3D, to simulate full spectral cubes of line emission from arbitrary PDRs in three dimensions (3D). The model will reproduce the intensity of the main cooling lines from the Orion Bar PDR and the observed layered structure of the different transitions. Methods. We built up a 3D compound, made of voxels (3D pixels) that contain a discrete mass distribution of spherical clumpy structures, approximating the fractal ISM. To analyse each individual clump the new code was combined with the KOSMA-iota PDR model. Probabilistic algorithms were used to calculate the local FUV flux for each voxel as well as the voxel-averaged line emissivities and optical depths, based on the properties of the individual clumps. Finally, the computation of the radiative transfer through the compound provided full spectral cubes. To test the new model we tried to simulate the structure of the Orion Bar PDR and compared the results to observations from HIFI/Herschel and from the Caltech Submillimetre Observatory (CSO). In this context new Herschel data from the HEXOS guaranteed-time key program is presented. Results. Our model is able to reproduce the line-integrated intensities within a factor of 2.5 and the observed stratification pattern within 0.016 pc for the [CII] 158 mu m and different (CO)-C-12/13 and HCO+ transitions, based on the representation of the Orion Bar PDR by a clumpy edge-on cavity wall. In the cavity wall, a large fraction of the total mass needs to be contained in clumps. The mass of the interclump medium is constrained by the FUV penetration. Furthermore, the stratification profile cannot be reproduced by a model that has the same amount of clump and interclump mass in each voxel; dense clumps need to be removed from the PDR surface.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Andree-Labsch, S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Ossenkopf-Okada, V. UNSPECIFIED UNSPECIFIED UNSPECIFIED Roellig, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-240227
DOI:	10.1051/0004-6361/201424287
Journal or Publication Title:	Astron. Astrophys.
Volume:	598
Date:	2017
Publisher:	EDP SCIENCES S A
Place of Publication:	LES ULIS CEDEX A
ISSN:	1432-0746
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language PHOTODISSOCIATION REGIONS; MOLECULAR CLOUDS; INTERSTELLAR-MEDIUM; M17 SW; C-II; SUBMILLIMETER OBSERVATIONS; CHEMICAL STRATIFICATION; COLOGNE DATABASE; LINE EMISSION; MASS-SPECTRA Multiple languages Astronomy & Astrophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/24022