Simulating star clusters across cosmic time - I. Initial mass function, star formation rates, and efficiencies
Abstract
We present radiation-magneto-hydrodynamic simulations of star formation in self-gravitating, turbulent molecular clouds, modelling the formation of individual massive stars, including their UV radiation feedback. The set of simulations have cloud masses between mgas = 103 M⊙ and 3 × 105 M⊙ and gas densities typical of clouds in the local Universe (\overline{n}_gas ∼ 1.8× 10^2 cm-3) and 10× and 100× denser, expected to exist in high-redshift galaxies. The main results are as follows. (i) The observed Salpeter power-law slope and normalization of the stellar initial mass function at the high-mass end can be reproduced if we assume that each star-forming gas clump (sink particle) fragments into stars producing on average a maximum stellar mass about 40{{ per cent}} of the mass of the sink particle, while the remaining 60{{ per cent}} is distributed into smaller mass stars. Assuming that the sinks fragment according to a power-law mass function flatter than Salpeter, with log-slope 0.8, satisfy this empirical prescription. (ii) The star formation law that best describes our set of simulation is dρ _*/dt ∝ ρ _gas^{1.5} if \overline{n}_gas< n_cri≈ 10^3 cm-3, and dρ _*/dt ∝ ρ _gas^{2.5} otherwise. The duration of the star formation episode is roughly six cloud's sound crossing times (with cs = 10 km s-1). (iii) The total star formation efficiency in the cloud is f_*=2{{ per cent}} (m_gas/10^4 M_\odot)^{0.4}(1+\overline{n}_gas/n_cri)^{0.91}, for gas at solar metallicity, while for metallicity Z < 0.1 Z⊙, based on our limited sample, f* is reduced by a factor of ∼5. (iv) The most compact and massive clouds appear to form globular cluster progenitors, in the sense that star clusters remain gravitationally bound after the gas has been expelled.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- October 2019
- DOI:
- 10.1093/mnras/stz2239
- arXiv:
- arXiv:1904.07889
- Bibcode:
- 2019MNRAS.489.1880H
- Keywords:
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- stars: formation;
- stars: luminosity function;
- mass function;
- ISM: clouds;
- H <sc>ii</sc> regions;
- globular clusters: general;
- galaxies: high-redshift;
- galaxies: star clusters: general;
- galaxies: star formation;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 21 pages, 18 figures, Published in MNRAS. References added