Universität zu Köln

Joblin, C., Bron, E., Pinto, C., Pilleri, P., Le Petit, F., Gerin, M., Le Bourlot, J., Fuente, A., Berne, O., Goicoechea, J. R., Habart, E., Kohler, M., Teyssier, D., Nagy, Z., Montillaud, J., Vastel, C., Cernicharo, J., Roellig, M., Ossenkopf-Okada, V. and Bergin, E. A. (2018). Structure of photodissociation fronts in star-forming regions revealed by Herschel observations of high-J CO emission lines. Astron. Astrophys., 615. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

Context. In bright photodissociation regions (PDR) associated with massive star formation, the presence of dense clumps that are immersed in a less dense interclump medium is often proposed to explain the difficulty of models to account for the observed gas emission in high-excitation lines. Aims. We aim to present a comprehensive view of the modelling of the CO rotational ladder in PDRs, including the high-J lines that trace warm molecular gas at PDR interfaces. Methods. We observed the (CO)-C-12 and (CO)-C-13 ladders in two prototypical PDRs, the Orion Bar and NGC7023 NW using the instruments onboard Herschel. We also considered line emission from key species in the gas cooling of PDRs (C+, O, and H-2) and other tracers of PDR edges such as OH and CH+. All the intensities are collected from Herschel observations, the literature and the Spitzer archive and were analysed using the Meudon PDR code. Results. A grid of models was run to explore the parameter space of only two parameters: thermal gas pressure and a global scaling factor that corrects for approximations in the assumed geometry. We conclude that the emission in the high-J CO lines, which were observed up to J(up) = 23 in the Orion Bar (J(up) = 19 in NGC7023), can only originate from small structures with typical thicknesses of a few 10(-3) pc and at high thermal pressures (P-th similar to 10(8) Kcm(-3)). Conclusions. Compiling data from the literature, we find that the gas thermal pressure increases with the intensity of the UV radiation field given by G(0), following a trend in line with recent simulations of the photoevaporation of illuminated edges of molecular clouds. This relation can help to rationalise the analysis of high-J CO emission in massive star formation and provides an observational constraint for models which study stellar feedback on molecular clouds.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Joblin, C. UNSPECIFIED UNSPECIFIED UNSPECIFIED Bron, E. UNSPECIFIED UNSPECIFIED UNSPECIFIED Pinto, C. UNSPECIFIED UNSPECIFIED UNSPECIFIED Pilleri, P. UNSPECIFIED UNSPECIFIED UNSPECIFIED Le Petit, F. UNSPECIFIED UNSPECIFIED UNSPECIFIED Gerin, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Le Bourlot, J. UNSPECIFIED UNSPECIFIED UNSPECIFIED Fuente, A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Berne, O. UNSPECIFIED UNSPECIFIED UNSPECIFIED Goicoechea, J. R. UNSPECIFIED UNSPECIFIED UNSPECIFIED Habart, E. UNSPECIFIED UNSPECIFIED UNSPECIFIED Kohler, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Teyssier, D. UNSPECIFIED UNSPECIFIED UNSPECIFIED Nagy, Z. UNSPECIFIED UNSPECIFIED UNSPECIFIED Montillaud, J. UNSPECIFIED UNSPECIFIED UNSPECIFIED Vastel, C. UNSPECIFIED UNSPECIFIED UNSPECIFIED Cernicharo, J. UNSPECIFIED UNSPECIFIED UNSPECIFIED Roellig, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Ossenkopf-Okada, V. UNSPECIFIED UNSPECIFIED UNSPECIFIED Bergin, E. A. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-179454
DOI:	10.1051/0004-6361/201832611
Journal or Publication Title:	Astron. Astrophys.
Volume:	615
Date:	2018
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 ULTRAVIOLET EXTINCTION CURVES; NEAR-INFRARED SPECTROSCOPY; PHOTON-DOMINATED REGIONS; ORION BAR; MOLECULAR CLOUD; CLUMPY STRUCTURE; H-2 FORMATION; M17 SW; H-I; RADIATION Multiple languages Astronomy & Astrophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/17945