Universität zu Köln

Perez-Beaupuits, J. P., Stutzki, J., Ossenkopf, V., Spaans, M., Guesten, R. and Wiesemeyer, H. (2015). Detection of a large fraction of atomic gas not associated with star-forming material in M17 SW. Astron. Astrophys., 575. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

Context. The [C II] 158 mu m line is one of the dominant coolants of the ISM, and an important probe with which to study the star formation process. Recent Herschel/HIFI and SOFIA/GREAT observations showed that assuming the total velocity-integrated intensity of this line is directly associated with the star-forming material is inadequate. Aims. We probe the column densities and masses traced by the ionized and neutral atomic carbon with spectrally resolved maps, and compare them to the diffuse and dense molecular gas traced by [C I] and low-J CO lines toward the star-forming region M17 SW. Methods. We mapped a 4.1 pc x 4.7 pc region in the [C I] 609 mu m line using the APEX telescope, as well as the CO isotopologues with the IRAM 30 m telescope. Because of the velocity-resolved spectra, we analyze the data based on velocity channel maps that are 1 km s(-1) wide. We correlate their spatial distribution with that of the [C II] map obtained with SOFIA/GREAT. Optically thin approximations were used to estimate the column densities of [C I] and [C II] in each velocity channel. Results. The distribution of the emission from the isotopologues (CO)-C-13, (CO)-O-17, and (CO)-O-18 resembles more closely that of the [C I] emission than that of the (CO)-C-12 emission. The spatial distribution of the [C I] and all CO isotopologues emission was found to be associated with that of [C II] in about 20%-80% of the mapped region, with the high correlation found in the central (15-23 km s(-1)) velocity channels. Conclusions. The excitation temperature of [C I] ranges between 40 K and 100 K in the inner molecular region of M17 SW. Excitation temperatures up to 200 K are found along the ridge. Column densities in 1 km s(-1) channels between similar to 10(15) cm(-2) and similar to 10(17) cm-2 were found for [C I]. Just similar to 20 % of the velocity range (similar to 40 km s(-1)) that the [C II] line spans is associated with the star-forming material traced by [C I] and CO. The total ( integrated over the 0-40 km s(-1) velocity range) gas mass estimated from the [C II] emission gives a lower limit of similar to 4.4 x 10(3) M-circle dot. A very large fraction of at least 64% of this mass is not associated with the star-forming material in M17 SW. We also found that about 36%, 17%, and 47% of the [C II] emission is associated with the H II, H I, and H-2 regimes, respectively. Comparisons with the H41 alpha line shows an ionization region mixed with the neutral and part of the molecular gas, in agreement with the clumped structure and dynamical processes at play in M17 SW. These results are also relevant to extra-galactic studies in which [C II] is often used as a tracer of star-forming material.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Perez-Beaupuits, J. P. UNSPECIFIED UNSPECIFIED UNSPECIFIED Stutzki, J. UNSPECIFIED UNSPECIFIED UNSPECIFIED Ossenkopf, V. UNSPECIFIED UNSPECIFIED UNSPECIFIED Spaans, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Guesten, R. UNSPECIFIED UNSPECIFIED UNSPECIFIED Wiesemeyer, H. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-406042
DOI:	10.1051/0004-6361/201425020
Journal or Publication Title:	Astron. Astrophys.
Volume:	575
Date:	2015
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 PHOTON-DOMINATED REGIONS; 158 MU-M; C-II; PHOTODISSOCIATION REGIONS; INTERSTELLAR-MEDIUM; STELLAR POPULATION; LINE OBSERVATIONS; CLUMPY STRUCTURE; DENSE GAS; WARM GAS Multiple languages Astronomy & Astrophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/40604