Feedback-regulated star formation in molecular clouds and galactic discs
Abstract
We present a two-zone theory for feedback-regulated star formation in galactic discs, consistently connecting the galaxy-averaged star formation law with star formation proceeding in giant molecular clouds (GMCs). Our focus is on galaxies with gas surface density Σ_g ≳ 100 M_⊙ pc⁻², where the interstellar medium (ISM) can be assumed to be fully molecular. This regime includes most star formation in the Universe and our basic framework can be extended to other galaxies. In our theory, the galactic disc consists of Toomre-mass GMCs embedded in a volume-filling ISM. Radiation pressure on dust disperses GMCs and most supernovae explode in the volume-filling medium. A galaxy-averaged star formation law is derived by balancing the momentum input from supernova feedback with the vertical gravitational weight of the disc gas. This star formation law is in good agreement with observations for a CO conversion factor depending continuously on Σg. We argue that the galaxy-averaged star formation efficiency per free-fall time, ϵᵍᵃˡ_(ff), is only a weak function of the efficiency with which GMCs convert their gas into stars, ϵ^(GMC)_(int). This is possible because the rate limiting step for star formation is the rate at which GMCs form: for large efficiency of star formation in GMCs, the Toomre Q parameter obtains a value slightly above unity so that the GMC formation rate is consistent with the galaxy-averaged star formation law. We contrast our results with other theories of turbulence-regulated star formation and discuss predictions of our model. Using a compilation of data from the literature, we show that the galaxy-averaged star formation efficiency per free-fall time is non-universal and increases with increasing gas fraction, as predicted by our model. We also predict that the fraction of the disc gas mass in bound GMCs decreases for increasing values of the GMC star formation efficiency. This is qualitatively consistent with the smooth molecular gas distribution inferred in local ultraluminous infrared galaxies and the small mass fraction in giant clumps in high-redshift galaxies.
Additional Information
© 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2013 May 14. Received 2013 April 28; in original form 2013 January 15. We thank Reinhard Genzel and Linda Tacconi for providing their compilation of gas and star formation rate measurements in electronic form. Ken Shen performed simulations of SNRs that informed our discussion of the momentum input by SNe. We are also grateful to Leo Blitz for a discussion on the possibility of measuring f_(GMC) in local galaxies and to Jacob Lynn for help with understanding large-scale turbulent fluctuations in supersonic turbulence. CAFG was supported by a fellowship from the Miller Institute for Basic Research in Science and NASA grant 10-ATP10-0187. EQ was supported by a Simons Investigator award from the Simons Foundation, the David and Lucile Packard Foundation, and the Thomas Alison Schneider Chair in Physics at UC Berkeley. Support for PFH was provided by NASA through Einstein Postdoctoral Fellowship Award Number PF1-120083 issued by the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the NASA under contract NAS8-03060.Attached Files
Published - stt866.pdf
Accepted Version - 1301.3905.pdf
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Additional details
- Eprint ID
- 103405
- Resolver ID
- CaltechAUTHORS:20200522-113948620
- Miller Institute for Basic Research in Science
- 10-ATP10-0187
- NASA
- Simons Foundation
- David and Lucile Packard Foundation
- University of California, Berkeley
- PF1-120083
- NASA Einstein Fellowship
- NAS8-03060
- NASA
- Created
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2020-05-22Created from EPrint's datestamp field
- Updated
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2021-11-16Created from EPrint's last_modified field