On the nature of variations in the measured star formation efficiency of molecular clouds

Michael Y. Grudic; Philip F. Hopkins; Eve J. Lee; Norman Murray; Claude André Faucher-Giguère; L. Clifton Johnson

doi:10.1093/mnras/stz1758

On the nature of variations in the measured star formation efficiency of molecular clouds

Michael Y. Grudic^*, Philip F. Hopkins, Eve J. Lee, Norman Murray, Claude André Faucher-Giguère, L. Clifton Johnson

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

46 Scopus citations

Abstract

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 (${\ll} 1\hbox{ per cent}$) are 'real' but correspond to early stages; the true 'per-freefall' SFE where most stars actually form can be much larger. Very high (${\gg} 10\hbox{ per cent}$) 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.

Original language	English (US)
Pages (from-to)	1501-1518
Number of pages	18
Journal	Monthly Notices of the Royal Astronomical Society
Volume	488
Issue number	2
DOIs	https://doi.org/10.1093/mnras/stz1758
State	Published - Jun 26 2019

Funding

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).

Keywords

H II regions
ISM: clouds
galaxies: star formation
stars: formation

ASJC Scopus subject areas

Astronomy and Astrophysics
Space and Planetary Science

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10.1093/mnras/stz1758

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title = "On the nature of variations in the measured star formation efficiency of molecular clouds",

abstract = "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 (${\ll} 1\hbox{ per cent}$) are 'real' but correspond to early stages; the true 'per-freefall' SFE where most stars actually form can be much larger. Very high (${\gg} 10\hbox{ per cent}$) 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.",

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On the nature of variations in the measured star formation efficiency of molecular clouds

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