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Tracing the Conversion of Gas into Stars in Young Massive Cluster Progenitors

Walker, DL and Longmore, SN and Bastian, N and Kruijssen, JMD and Rathborne, JM and Jackson, JM and Foster, JB and Contreras, Y (2015) Tracing the Conversion of Gas into Stars in Young Massive Cluster Progenitors. Monthly Notices of the Royal Astronomical Society, 449 (1). pp. 715-725. ISSN 0035-8711

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Abstract

Whilst young massive clusters (YMCs; $M$ $\gtrsim$ 10$^{4}$ M$_{\odot}$, age $\lesssim$ 100 Myr) have been identified in significant numbers, their progenitor gas clouds have eluded detection. Recently, four extreme molecular clouds residing within 200 pc of the Galactic centre have been identified as having the properties thought necessary to form YMCs. Here we utilise far-IR continuum data from the Herschel Infrared Galactic Plane Survey (HiGAL) and millimetre spectral line data from the Millimetre Astronomy Legacy Team 90 GHz Survey (MALT90) to determine their global physical and kinematic structure. We derive their masses, dust temperatures and radii and use virial analysis to conclude that they are all likely gravitationally bound -- confirming that they are likely YMC progenitors. We then compare the density profiles of these clouds to those of the gas and stellar components of the Sagittarius B2 Main and North proto-clusters and the stellar distribution of the Arches YMC. We find that even in these clouds -- the most massive and dense quiescent clouds in the Galaxy -- the gas is not compact enough to form an Arches-like ($M$ = 2x10$^{4}$ M$_{\odot}$, R$_{eff}$ = 0.4 pc) stellar distribution. Further dynamical processes would be required to condense the resultant population, indicating that the mass becomes more centrally concentrated as the (proto)-cluster evolves. These results suggest that YMC formation may proceed hierarchically rather than through monolithic collapse.

Item Type: Article
Additional Information: This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record MNRAS (May 01, 2015) 449 (1): 715-725 is available online at: http:dx.doi.org/10.1093/mnras/stv300
Uncontrolled Keywords: astro-ph.GA; astro-ph.GA
Subjects: Q Science > QB Astronomy
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
Related URLs:
Date Deposited: 04 Mar 2015 11:18
Last Modified: 25 Jun 2015 12:37
URI: http://researchonline.ljmu.ac.uk/id/eprint/595

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