A Caltech Library Service

Clumpy outer Galaxy molecular clouds and the steepening of the IMF

Brand, J. and Wouterloot, J. G. A. and Rudolph, A. L. and de Geus, E. J. (2001) Clumpy outer Galaxy molecular clouds and the steepening of the IMF. Astronomy and Astrophysics, 377 (2). pp. 644-671. ISSN 0004-6361. doi:10.1051/0004-6361:20011057.

[img] PDF - Published Version
See Usage Policy.

[img] PDF - Accepted Version
See Usage Policy.


Use this Persistent URL to link to this item:


We report the results of high-resolution (~0.2 pc) CO (1-0) and CS (2-1) observations of the central regions of three star-forming molecular clouds in the far-outer Galaxy (~16 kpc from the Galactic Center): WB89 85 (Sh 2-127), WB89 380, and WB89 437. We used the BIMA array in combination with IRAM 30-m and NRAO 12-m observations. The GMC's in which the regions are embedded were studied by means of KOSMA 3-m CO (2-1) observations (here we also observed WB89 399). We compare the BIMA maps with optical, radio, and near-infrared observations. Using a clumpfind routine, structures found in the CO and CS emission are subdivided in clumps, the properties of which are analyzed and compared with newly derived results of previously published single-dish measurements of local clouds (OrionB South and Rosette). We find that the slopes of the clump mass distributions (-1.28 and -1.49, for WB89 85 and WB89 380, respectively) are somewhat less steep than found for most local clouds, but similar to those of clouds which have been analyzed with the same clumpfind program. We investigate the clump stability by using the virial theorem, including all possible contributions (gravity, turbulence, magnetic fields, and pressure due to the interclump gas). It appears that under reasonable assumptions a combination of these forces would render most clumps stable. Comparing only gravity and turbulence, we find that in the far-outer Galaxy clouds, these forces are in equilibium (virial parameter α ≈ 1) for clumps down to the lowest masses found (a few M⊙). For clumps in the local clouds α ≈ 1 only for clumps with masses larger than a few tens of M⊙. Thus it appears that in these outer Galaxy clumps gravity is the dominant force down to a much lower mass than in local clouds, implying that gravitational collapse and star formation may occur more readily even in the smallest clumps. Although there are some caveats, due to the inhomogeneity of the data used, this might explain the apparently steeper IMF found in the outer Galaxy.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Additional Information:© 2001 ESO. Article published by EDP Sciences. Received 7 September 2000; Accepted 24 July 2001; Published online 15 October 2001. E. dG., J. B., and J. G. A. W. acknowledge support from NATO grant 920835. E. dG. acknowledges financial support from NSF grant AST-8918912 and NASA grant NAG 5-1736. A. L. R. acknowledges the support of the NSF Young Faculty Career Development CAREER Program via NSF grant 96-24924. This work was completed while J. G. A. W. was a Visiting Professor at the Istituto di Radioastronomia, CNR, Bologna. We thank Jonathan Williams, Carsten Kramer, and Nicola Schneider for generously making their original data available for analysis, and Malcolm Walmsley and Leo Blitz for commenting on an earlier version of this paper. Jonathan Williams is also thanked for providing us with the latest version of CLUMPFIND, running in IDL, and for patiently answering our questions about this procedure. The KOSMA radio telescope at Gornergrat-Süd Observatory is operated by the University of Köln, and supported by the Deutsche Forschungsgemeinschaft through grant SFB-301, as well as by special funding from the Land Nordrhein-Westfalen. The Observatory is administered by the Internationale Stiftung Hochalpine Forschungsstationen Jungfraujoch und Gornergrat, Bern, Switzerland.
Funding AgencyGrant Number
North Atlantic Treaty Organization (NATO)920835
NASANAG 5-1736
Deutsche Forschungsgemeinschaft (DFG)SFB-301
Land Nordrhein-WestfalenUNSPECIFIED
Subject Keywords:ISM: clouds - molecules - radio lines: ISM
Issue or Number:2
Record Number:CaltechAUTHORS:20180213-155146078
Persistent URL:
Official Citation:Clumpy outer Galaxy molecular clouds and the steepening of the IMF J. Brand, J. G. A. Wouterloot, A. L. Rudolph and E. J. de Geus A&A, 377 2 (2001) 644-671. DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:84816
Deposited By: Tony Diaz
Deposited On:14 Feb 2018 00:21
Last Modified:15 Nov 2021 20:23

Repository Staff Only: item control page