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On The Nature of Variations in the Measured Star Formation Efficiency of Molecular Clouds

Grudić, Michael Y. and Hopkins, Philip F. and Lee, Eve J. and Murray, Norman and Faucher-Giguère, Claude-André and Johnson, L. Clifton (2019) On The Nature of Variations in the Measured Star Formation Efficiency of Molecular Clouds. Monthly Notices of the Royal Astronomical Society, 488 (2). pp. 1501-1518. ISSN 0035-8711. doi:10.1093/mnras/stz1758.

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Measurements of the star formation efficiency (SFE) of giant molecular clouds (GMCs) in the Milky Way generally show a large scatter, which could be intrinsic or observational. We use magnetohydrodynamic simulations of GMCs (including feedback) to forward-model the relationship between the true GMC SFE and observational proxies. We show that individual GMCs trace broad ranges of observed SFE throughout collapse, star formation, and disruption. Low measured SFEs (⁠≪1 per cent⁠) are ‘real’ but correspond to early stages; the true ‘per-freefall’ SFE where most stars actually form can be much larger. Very high (⁠≫10 per cent⁠) values are often artificially enhanced by rapid gas dispersal. Simulations including stellar feedback reproduce observed GMC-scale SFEs, but simulations without feedback produce 20× larger SFEs. Radiative feedback dominates among mechanisms simulated. An anticorrelation of SFE with cloud mass is shown to be an observational artefact. We also explore individual dense ‘clumps’ within GMCs and show that (with feedback) their bulk properties agree well with observations. Predicted SFEs within the dense clumps are ∼2× larger than observed, possibly indicating physics other than feedback from massive (main-sequence) stars is needed to regulate their collapse.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Grudić, Michael Y.0000-0002-1655-5604
Hopkins, Philip F.0000-0003-3729-1684
Lee, Eve J.0000-0002-1228-9820
Faucher-Giguère, Claude-André0000-0002-4900-6628
Additional Information:© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2019 June 12. Received 2019 May 8; in original form 2018 September 21. Published: 26 June 2019. We thank Neal J. Evans II, Mark Krumholz, Diederik Kruijssen, Marta Reina-Campos, and Sharon Meidt for enlightening discussions that informed and motivated this work. We also thank Shea Garrison-Kimmel and Alex Gurvich for helpful suggestions for data presentation and visualization. Support for MYG and PFH was provided by a James A Cullen Memorial Fellowship, an Alfred P. Sloan Research Fellowship, NSF Collaborative Research Grant #1715847 and CAREER grant #1455342, and NASA grants NNX15AT06G, JPL 1589742, 17-ATP17-0214. CAFG was supported by NSF through grants AST-1412836, AST-1517491, AST-1715216, and CAREER award AST-1652522, by NASA through grant NNX15AB22G, and by a Cottrell Scholar Award from the Research Corporation for Science Advancement. NM acknowledges the support of the Natural Sciences and Engineering Research Council of Canada (NSERC). This research was undertaken, in part, thanks to funding from the Canada Research Chairs program. NM’s work was performed in part at the Aspen Center for Physics, which is supported by National Science Foundation grant PHY-1607611. Numerical calculations were run on the Caltech compute cluster ‘Wheeler’, allocations from XSEDE TG-AST130039 and PRAC NSF.1713353 (awards OCI-0725070 and ACI-1238993) supported by the NSF, and NASA HEC SMD-16-7592. This research has made use of NASA’s Astrophysics Data System, IPYTHON (Pérez & Granger 2007), NUMPY, SCIPY (Jones et al. 2001), and MATPLOTLIB (Hunter 2007).
Group:TAPIR, Astronomy Department
Funding AgencyGrant Number
James A. Cullen Memorial FellowshipUNSPECIFIED
Alfred P. Sloan FoundationUNSPECIFIED
Cottrell Scholar of Research CorporationUNSPECIFIED
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
Canada Research Chairs ProgramUNSPECIFIED
Subject Keywords:stars: formation – ISM: clouds –HII regions – galaxies: star formation
Issue or Number:2
Record Number:CaltechAUTHORS:20190206-105603989
Persistent URL:
Official Citation:Michael Y Grudić, Philip F Hopkins, Eve J Lee, Norman Murray, Claude-André Faucher-Giguère, L Clifton Johnson, On the nature of variations in the measured star formation efficiency of molecular clouds, Monthly Notices of the Royal Astronomical Society, Volume 488, Issue 2, September 2019, Pages 1501–1518,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:92720
Deposited By: George Porter
Deposited On:08 Feb 2019 18:25
Last Modified:16 Nov 2021 03:52

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