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Massive 70μm quiet clumps – II. non-thermal motions driven by gravity in massive star formation?

Traficante, A., Fuller, G. A., Smith, R. J., Billot, N., Duarte Cabral, Ana, Peretto, Nicolas, Molinari, S. and Pineda, J. E. 2018. Massive 70μm quiet clumps – II. non-thermal motions driven by gravity in massive star formation? Monthly Notices of the Royal Astronomical Society 473 (4) , pp. 4975-4985. 10.1093/mnras/stx2672

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Abstract

The dynamic activity in massive star-forming regions prior to the formation of bright protostars is still not fully investigated. In this work, we present observations of HCO+J = 1–0 and N2H+J = 1–0 made with the IRAM 30  m telescope towards a sample of 16 Herschel-identified massive 70 μm quiet clumps associated with infrared dark clouds. The clumps span a mass range from 300 to 2000 M⊙. The N2H+ data show that the regions have significant non-thermal motions with velocity dispersion between 0.28 and 1.5 km s−1, corresponding to Mach numbers between 2.6 and 11.5. The majority of the 70 μm quiet clumps have asymmetric HCO+ line profiles, indicative of significant dynamical activity. We show that there is a correlation between the degree of line asymmetry and the surface density Σ of the clumps, with clumps of Σ ≳ 0.1 g cm−2 having more asymmetric line profiles, and so are more dynamically active, than clumps with lower Σ. We explore the relationship between velocity dispersion, radius and Σ and show how it can be interpreted as a relationship between an acceleration generated by the gravitational field, aG, and the measured kinetic acceleration, ak, consistent with the majority of the non-thermal motions originating from self-gravity. Finally, we consider the role of external pressure and magnetic fields in the interplay of forces.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Subjects: Q Science > QB Astronomy
Publisher: Oxford University Press
ISSN: 0035-8711
Date of First Compliant Deposit: 20 December 2017
Date of Acceptance: 8 October 2017
Last Modified: 20 Dec 2017 12:02
URI: http://orca.cf.ac.uk/id/eprint/107697

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