Can the removal of molecular cloud envelopes by external feedback affect the efficiency of star formation?
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We investigate how star formation efficiency can be significantly decreased by the removal of a molecular cloud’s envelope by feedback from an external source. Feedback from star formation has difficulties halting the process in dense gas but can easily remove the less dense and warmer envelopes where star formation does not occur. However, the envelopes can play an important role keeping their host clouds bound by deepening the gravitational potential and providing a constraining pressure boundary. We use numerical simulations to show that removal of the cloud envelopes results in all cases in a fall in the star formation efficiency (SFE). At 1.38 free-fall times our 4 pc cloud simulation experienced a drop in the SFE from 16 to six percent, while our 5 pc cloud fell from 27 to 16 per cent. At the same time, our 3 pc cloud (the least bound) fell from an SFE of 5.67 per cent to zero when the envelope was lost. The star formation efficiency per free-fall time varied from zero to ≈0.25 according to α, defined to be the ratio of the kinetic plus thermal to gravitational energy, and irrespective of the absolute star forming mass available. Furthermore the fall in SFE associated with the loss of the envelope is found to even occur at later times. We conclude that the SFE will always fall should a star forming cloud lose its envelope due to stellar feedback, with less bound clouds suffering the greatest decrease.
Lucas , W E , Bonnell , I A & Forgan , D H 2017 , ' Can the removal of molecular cloud envelopes by external feedback affect the efficiency of star formation? ' Monthly Notices of the Royal Astronomical Society . DOI: 10.1093/mnras/stx073
Monthly Notices of the Royal Astronomical Society
© 2017, the Author(s). This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at academic.oup.com/mnras / https://doi.org/10.1093/mnras/stx073
The authors thank Paul Clark for his contribution towards the original concept of this paper and the anonymous referee for their helpful comments. Our column density plots were produced using Daniel Price’s SPLASH software (Price 2007). The authors gratefully acknowledge support from the ECOGAL project, grant agreement 291227, funded by the European Research Council under ERC-2011-ADG. This work used the compute resources of the St Andrews MHD Cluster. This work used the DiRAC Complexity system, operated by the University of Leicester IT Services, which forms part of the STFC DiRAC HPC Facility (www.dirac.ac.uk). This equipment is funded by BIS National E-Infrastructure capital grant ST/K000373/1 and STFC DiRAC Operations grant ST/K0003259/1. DiRAC is part of the National E-Infrastructure.
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