How Galaxies Form Stars: The Connection between Local and Global Star Formation in Galaxy Simulations

Journal Article · Tue Jun 26 00:00:00 EDT 2018 · The Astrophysical Journal (Online)

DOI:https://doi.org/10.3847/1538-4357/aac6eb· OSTI ID:1469371

Semenov, Vadim A.  ^[1]; Kravtsov, Andrey V.  ^[1]; Gnedin, Nickolay Y. ^[2]

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1. The Univ. of Chicago, Chicago, IL (United States)
2. The Univ. of Chicago, Chicago, IL (United States); Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)

Using a suite of isolated $$L_\star$$ galaxy simulations, we show that global depletion times and star-forming gas mass fractions in simulated galaxies exhibit systematic and well-defined trends as a function of the local star formation efficiency per freefall time, $$\epsilon_{\rm ff}$$, strength of stellar feedback, and star formation threshold. We demonstrate that these trends can be reproduced and explained by a simple physical model of global star formation in galaxies. Our model is based on mass conservation and the idea of gas cycling between star-forming and non-star-forming states on certain characteristic time scales under the influence of dynamical and feedback processes. Both the simulation results and our model predictions exhibit two limiting regimes with rather different dependencies of global galactic properties on the local parameters. When $$\epsilon_{\rm ff}$$ is small and feedback is inefficient, the total star-forming mass fraction, $$f_{\rm sf}$$, is independent of $$\epsilon_{\rm ff}$$ and the global depletion time, $$\tau_{\rm dep}$$, scales inversely with $$\epsilon_{\rm ff}$$. When $$\epsilon_{\rm ff}$$ is large or feedback is very efficient, these trends are reversed: $$f_{\rm sf} \propto \epsilon_{\rm ff}^{-1}$$ and $$\tau_{\rm dep}$$ is independent of $$\epsilon_{\rm ff}$$ but scales linearly with the feedback strength. We also compare our results with the observed depletion times and mass fractions of star-forming and molecular gas and show that they provide complementary constraints on $$\epsilon_{\rm ff}$$ and the feedback strength. In conclusion, we show that useful constraints on $$\epsilon_{\rm ff}$$ can also be obtained using measurements of the depletion time and its scatter on different spatial scales.

• Research Organization: Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), High Energy Physics (HEP)
• Grant/Contract Number: AC02-07CH11359
• OSTI ID: 1469371
• Report Number(s): arXiv:1803.00007; FERMILAB-PUB-18-365-A; 1684463
• Journal Information: The Astrophysical Journal (Online), Vol. 861, Issue 1; ISSN 1538-4357
• Publisher: Institute of Physics (IOP)
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
galaxies: evolution
ISM: kinematics and dynamics
methods: numerical
stars: formation