What Sets the Star Formation Rate of Molecular Clouds? The Density Distribution as a Fingerprint of Compression and Expansion Rates

Journal Article · 25 August 2023 · The Astrophysical Journal

DOI: https://doi.org/10.3847/1538-4357/ace897 · OSTI ID:2425050

Appel, Sabrina M.  ^[1]; Burkhart, Blakesley  ^[2]; Semenov, Vadim A.  ^[3]; Federrath, Christoph  ^[4]; Rosen, Anna L.  ^[5]; Tan, Jonathan C.  ^[6]

---

1. Rutgers University, Piscataway, NJ (United States)
2. Rutgers University, Piscataway, NJ (United States); Flatiron Institute, New York, NY (United States)
3. Harvard & Smithsonian, Cambridge, MA (United States)
4. Australian National University, Canberra (Australia); Australian Research Council Centre of Excellence in All Sky Astrophysics (ASTRO3D), Canberra (Australia)
5. San Diego State University, CA (United States); University of California, San Diego, La Jolla, CA (United States)
6. Chalmers University of Technology, Gothenburg (Sweden); University of Virginia, Charlottesville, VA (United States)

We use a suite of 3D simulations of star-forming molecular clouds, with and without stellar feedback, magnetic fields, and driven turbulence, to study the compression and expansion rates of the gas as functions of density. We show that, around the mean density, supersonic turbulence promotes rough equilibrium between the amounts of compressing and expanding gas, consistent with continuous gas cycling between high- and low-density states. We find that the inclusion of protostellar jets produces rapidly expanding and compressing low-density gas. We find that the gas mass flux peaks at the transition between the lognormal and power-law forms of the density probability distribution function (PDF). This is consistent with the transition density tracking the post-shock density, which promotes an enhancement of mass at this density (i.e., shock compression and filament formation). At high densities, the gas dynamics are dominated by self-gravity: the compression rate in all of our runs matches the rate of the run with only gravity, suggesting that processes other than self-gravity have little effect at these densities. The net gas mass flux becomes constant at a density below the sink formation threshold, where it equals the star formation rate. The density at which the net gas mass flux equals the star formation rate is one order of magnitude lower than our sink threshold density, corresponds to the formation of the second power-law tail in the density PDF, and sets the overall star formation rates of these simulations.

• Research Organization: University of Chicago, IL (United States). DOE NNSA-ASC OASCR Flash Center
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC); National Science Foundation (NSF); National Aeronautics and Space Administration (NASA); Australian Research Council; Leibniz Rechenzentrum; Gauss Centre for Supercomputing; Australian National Computational Infrastructure
• OSTI ID: 2425050
• Journal Information: The Astrophysical Journal, Journal Name: The Astrophysical Journal Journal Issue: 1 Vol. 954; ISSN 0004-637X
• Publisher: IOP PublishingCopyright Statement
• Country of Publication: United States
• Language: English