Universität zu Köln

Wienen, M., Wyrowski, F., Menten, K. M., Urquhart, J. S., Walmsley, C. M., Csengeri, T., Koribalski, B. S. and Schuller, F. (2018). ATLASGAL - Ammonia observations towards the southern Galactic plane. Astron. Astrophys., 609. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

Context. The initial conditions of molecular clumps in which high-mass stars form are poorly understood. In particular, a more detailed study of the earliest evolutionary phases is needed. The APEX Telescope Large Area Survey of the whole inner Galactic disk at 870 mu m, ATLASGAL, has therefore been conducted to discover high-mass star-forming regions at different evolutionary phases. Aims. We derive properties such as velocities, rotational temperatures, column densities, and abundances of a large sample of southern ATLASGAL clumps in the fourth quadrant. Methods. Using the Parkes telescope, we observed the NH3 (1, 1) to (3, 3) inversion transitions towards 354 dust clumps detected by ATLASGAL within a Galactic longitude range between 300 degrees and 359 degrees and a latitude within +/- 1.5 degrees. For a subsample of 289 sources, the N2H+ (1-0) line was measured with the Mopra telescope. Results. We measured a median NH3 (1, 1) line width of similar to 2 km s(-1), rotational temperatures from 12 to 28 K with a mean of 18 K, and source-averaged NH3 abundances from 1.6 x 10(-6) to 10(-8). For a subsample with detected NH3 (2, 2) hyperfine components, we found that the commonly used method to compute the (2, 2) optical depth from the (1, 1) optical depth and the (2, 2) to (1, 1) main beam brightness temperature ratio leads to an underestimation of the rotational temperature and column density. A larger median virial parameter of similar to 1 is determined using the broader N2H+ line width than is estimated from the NH3 line width of similar to 0.5 with a general trend of a decreasing virial parameter with increasing gas mass. We obtain a rising NH3 (1, 1)/N2H+ line-width ratio with increasing rotational temperature. Conclusions. A comparison of NH3 line parameters of ATLASGAL clumps to cores in nearby molecular clouds reveals smaller velocity dispersions in low-mass than high-mass star-forming regions and a warmer surrounding of ATLASGAL clumps than the surrounding of low-mass cores. The NH3 (1, 1) inversion transition of 49% of the sources shows hyperfine structure anomalies. The intensity ratio of the outer hyperfine structure lines with a median of 1.27 +/- 0.03 and a standard deviation of 0.45 is significantly higher than 1, while the intensity ratios of the inner satellites with a median of 0.9 +/- 0.02 and standard deviation of 0.3 and the sum of the inner and outer hyperfine components with a median of 1.06 +/- 0.02 and standard deviation of 0.37 are closer to 1.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Wienen, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Wyrowski, F. UNSPECIFIED UNSPECIFIED UNSPECIFIED Menten, K. M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Urquhart, J. S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Walmsley, C. M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Csengeri, T. UNSPECIFIED UNSPECIFIED UNSPECIFIED Koribalski, B. S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Schuller, F. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-197011
DOI:	10.1051/0004-6361/201526384
Journal or Publication Title:	Astron. Astrophys.
Volume:	609
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 INFRARED-DARK CLOUDS; H-II REGIONS; MASSIVE STAR-FORMATION; GHZ METHANOL MASERS; DENSE CORE POPULATION; IRAS POINT SOURCES; MOLECULAR CLOUDS; PHYSICAL-PROPERTIES; CARBON-MONOXIDE; DUST-CONTINUUM Multiple languages Astronomy & Astrophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/19701