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The frequency and nature of 'cloud-cloud collisions' in galaxies

Dobbs, C. L., Pringle, J. E. and Duarte Cabral, Ana 2015. The frequency and nature of 'cloud-cloud collisions' in galaxies. Monthly Notices of the Royal Astronomical Society 446 (4) , p. 3608. 10.1093/mnras/stu2319

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Abstract

We investigate cloud–cloud collisions and giant molecular cloud evolution in hydrodynamic simulations of isolated galaxies. The simulations include heating and cooling of the interstellar medium (ISM), self-gravity and stellar feedback. Over time-scales <5 Myr most clouds undergo no change, and mergers and splits are found to be typically two-body processes, but evolution over longer time-scales is more complex and involves a greater fraction of intercloud material. We find that mergers or collisions occur every 8–10 Myr (1/15th of an orbit) in a simulation with spiral arms, and once every 28 Myr (1/5th of an orbit) with no imposed spiral arms. Both figures are higher than expected from analytic estimates, as clouds are not uniformly distributed in the galaxy. Thus, clouds can be expected to undergo between zero and a few collisions over their lifetime. We present specific examples of cloud–cloud interactions in our results, including synthetic CO maps. We would expect cloud–cloud interactions to be observable, but find they appear to have little or no impact on the ISM. Due to a combination of the clouds’ typical geometries, and moderate velocity dispersions, cloud–cloud interactions often better resemble a smaller cloud nudging a larger cloud. Our findings are consistent with the view that spiral arms make little difference to overall star formation rates in galaxies, and we see no evidence that collisions likely produce massive clusters. However, to confirm the outcome of such massive cloud collisions we ideally need higher resolution simulations.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Subjects: Q Science > QB Astronomy
Publisher: Oxford University Press
ISSN: 00358711
Date of First Compliant Deposit: 11 October 2017
Date of Acceptance: 30 October 2014
Last Modified: 22 Feb 2019 11:36
URI: http://orca-mwe.cf.ac.uk/id/eprint/105400

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