Universität zu Köln

Guevara, C., Stutzki, J., Ossenkopf-Okada, V, Simon, R., Perez-Beaupuits, J. P., Beuther, H., Bihr, S., Higgins, R., Graf, U. and Guesten, R. (2020). [C II] 158 mu m self-absorption and optical depth effects. Astron. Astrophys., 636. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

Context. The [CII] 158 mu m far-infrared fine-structure line is one of the most important cooling lines of the star-forming interstellar medium (ISM). It is used as a tracer of star formation efficiency in external galaxies and to study feedback effects in parental clouds. High spectral resolution observations have shown complex structures in the line profiles of the [CII] emission.Aims. Our aim is to determine whether the complex profiles observed in [(CII)-C-12] are due to individual velocity components along the line-of-sight or to self-absorption based on a comparison of the [(CII)-C-12] and isotopic [(CII)-C-13] line profiles.Methods. Deep integrations with the SOFIA/upGREAT 7-pixel array receiver in the sources of M43, Horsehead PDR, Monoceros R2, and M17 SW allow for the detection of optically thin [(CII)-C-13] emission lines, along with the [(CII)-C-12] emission lines, with a high signal-to-noise ratio. We first derived the [(CII)-C-12] optical depth and the [CII] column density from a single component model. However, the complex line profiles observed require a double layer model with an emitting background and an absorbing foreground. A multi-component velocity fit allows us to derive the physical conditions of the [CII] gas: column density and excitation temperature.Results. We find moderate to high [(CII)-C-12] optical depths in all four sources and self-absorption of [(CII)-C-12] in Mon R2 and M17 SW. The high column density of the warm background emission corresponds to an equivalent A(v) of up to 41 mag. The foreground absorption requires substantial column densities of cold and dense [CII] gas, with an equivalent A(v) ranging up to about 13 mag.Conclusions. The column density of the warm background material requires multiple photon-dominated region surfaces stacked along the line of sight and in velocity. The substantial column density of dense and cold foreground [CII] gas detected in absorption cannot be explained with any known scenario and we can only speculate on its origins.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Guevara, C. UNSPECIFIED UNSPECIFIED UNSPECIFIED Stutzki, J. UNSPECIFIED UNSPECIFIED UNSPECIFIED Ossenkopf-Okada, V UNSPECIFIED UNSPECIFIED UNSPECIFIED Simon, R. UNSPECIFIED UNSPECIFIED UNSPECIFIED Perez-Beaupuits, J. P. UNSPECIFIED UNSPECIFIED UNSPECIFIED Beuther, H. UNSPECIFIED UNSPECIFIED UNSPECIFIED Bihr, S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Higgins, R. UNSPECIFIED UNSPECIFIED UNSPECIFIED Graf, U. UNSPECIFIED UNSPECIFIED UNSPECIFIED Guesten, R. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-337418
DOI:	10.1051/0004-6361/201834380
Journal or Publication Title:	Astron. Astrophys.
Volume:	636
Date:	2020
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 C-12/C-13 ISOTOPE RATIO; X-RAY-OBSERVATION; INTERSTELLAR H-I; PHOTODISSOCIATION REGIONS; STELLAR POPULATION; ROSAT OBSERVATIONS; MOLECULAR CLOUDS; ALPHA ABSORPTION; ATOMIC CARBON; LINE Multiple languages Astronomy & Astrophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/33741