Star Cluster Formation in Cosmological Simulations. II. Effects of Star Formation Efficiency and Stellar Feedback

Journal Article · Mon Dec 04 00:00:00 EST 2017 · Astrophys.J.

DOI:https://doi.org/10.3847/1538-4357/aac9b8· OSTI ID:1469370

Li, Hui ^[1]; Gnedin, Oleg Y. ^[2]; Gnedin, Nickolay Y. ^[3]

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1. Michigan U.; MIT, Cambridge, Dept. Phys.; MIT, MKI
2. Michigan U.
3. Fermilab; Chicago U., KICP; Chicago U., Astron. Astrophys. Ctr.

The implementation of star formation and stellar feedback in cosmological simulations plays a critical role in shaping galaxy properties. In the first paper of the series, we presented a new method to model star formation as a collection of star clusters. In this paper, we improve the algorithm by eliminating accretion gaps, boosting momentum feedback, and introducing a subgrid initial bound fraction, $$f_i$$, that distinguishes cluster mass from stellar particle mass. We perform a suite of simulations with different star formation efficiency per freefall time $$\epsilon_{\rm ff}$$ and supernova momentum feedback intensity $$f_{\rm boost}$$. We find that the star formation history of a Milky Way-sized galaxy is sensitive to $$f_{\rm boost}$$, which allows us to constrain its value, $$f_{\rm boost}\approx5$$, in the current simulation setup. Changing $$\epsilon_{\rm ff}$$ from a few percent to 200\% has little effect on global galaxy properties. However, on smaller scales, the properties of star clusters are very sensitive to $$\epsilon_{\rm ff}$$. We find that $$f_i$$ increases with $$\epsilon_{\rm ff}$$ and cluster mass. Through the dependence on $$f_i$$, the shape of the cluster initial mass function varies strongly with $$\epsilon_{\rm ff}$$. The fraction of clustered star formation and maximum cluster mass increase with the star formation rate surface density, with the normalization of both relations dependent on $$\epsilon_{\rm ff}$$. The cluster formation timescale systematically decreases with increasing $$\epsilon_{\rm ff}$$. Local variations in the gas accretion history lead to a 0.25~dex scatter for the integral cluster formation efficiency. Joint constraints from all the observables prefer the runs that produce a median integral efficiency of 16\%.

• Research Organization: Chicago U., Astron. Astrophys. Ctr.; Chicago U., KICP; Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States); MIT, Cambridge, Dept. Phys.; MIT, MKI; Michigan U.
• Sponsoring Organization: US Department of Energy
• Grant/Contract Number: AC02-07CH11359
• OSTI ID: 1469370
• Report Number(s): FERMILAB-PUB-18-366-A; oai:inspirehep.net:1684467; arXiv:1712.01219
• Journal Information: Astrophys.J., Journal Name: Astrophys.J. Journal Issue: 2 Vol. 861
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
galaxies: formation
galaxies: high-redshift
galaxies: star clusters: general
galaxies: star formation
methods: numerical