Simulating Star Clusters Across Cosmic Time: I. Initial Mass Function, Star Formation Rates and Efficiencies. (arXiv:1904.07889v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+He_C/0/1/0/all/0/1">Chong-Chong He</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Ricotti_M/0/1/0/all/0/1">Massimo Ricotti</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Geen_S/0/1/0/all/0/1">Sam Geen</a> (2) ((1) Department of Astronomy, University of Maryland, College Park, MD, US, (2) Universit&#xe4;t Heidelberg, Zentrum f&#xfc;r Astronomie, Institut f&#xfc;r Theoretische Astrophysik, Heidelberg, Germany)

We present a large set of 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.
We consider a grid of simulations varying the cloud masses between m_gas = 10^3
M_sun to 3e5 M_sun, and resolving scales between 200 AU to 2000 AU. We consider
molecular clouds with gas mean number densities typical of those observed in
the local universe and denser molecular clouds expected to exist in
high-redshift galaxies.

In this paper, the first of a series, we focus on the analysis of the initial
mass function (IMF), the star formation rate (SFR), and the total star
formation efficiency (TSFE) in molecular clouds. These are the main results: i)
We find that the observed Salpeter power-law slope and normalisation of the
stellar IMF 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% of the mass of the sink particle,
while the remaining 60% is distributed into smaller mass stars. This empirical
prescription, and an IMF reproducing a Chabrier IMF, can be obtained assuming
that the sinks fragment according to a power-law mass function flatter than
Salpeter, with log-slope Gamma sim 0.8. This result is in agreement with the
observed mass function of dense cores in some molecular clouds. ii) The star
formation law that best describes our set of simulation is drho_*/dt ~
rho_gas^1.5 if n_gas
n_cri. The duration of the star formation episode of roughly 6 sound crossing
times of the cloud radius (with c_s=10 km/s). iii) For gas at solar metallicity
the TSFE in the cloud is f_*=2% (m_gas/10^4 M_sun)^0.4(1+n_gas/n_cri)^0.91,
also in agreement with (ii). [abridged]

We present a large set of 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.
We consider a grid of simulations varying the cloud masses between m_gas = 10^3
M_sun to 3e5 M_sun, and resolving scales between 200 AU to 2000 AU. We consider
molecular clouds with gas mean number densities typical of those observed in
the local universe and denser molecular clouds expected to exist in
high-redshift galaxies.

In this paper, the first of a series, we focus on the analysis of the initial
mass function (IMF), the star formation rate (SFR), and the total star
formation efficiency (TSFE) in molecular clouds. These are the main results: i)
We find that the observed Salpeter power-law slope and normalisation of the
stellar IMF 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% of the mass of the sink particle,
while the remaining 60% is distributed into smaller mass stars. This empirical
prescription, and an IMF reproducing a Chabrier IMF, can be obtained assuming
that the sinks fragment according to a power-law mass function flatter than
Salpeter, with log-slope Gamma sim 0.8. This result is in agreement with the
observed mass function of dense cores in some molecular clouds. ii) The star
formation law that best describes our set of simulation is drho_*/dt ~
rho_gas^1.5 if n_gas<n_cri ~ 10^3 cm^-3, and drho_*/dt ~ rho_gas^2.5 if n_gas >
n_cri. The duration of the star formation episode of roughly 6 sound crossing
times of the cloud radius (with c_s=10 km/s). iii) For gas at solar metallicity
the TSFE in the cloud is f_*=2% (m_gas/10^4 M_sun)^0.4(1+n_gas/n_cri)^0.91,
also in agreement with (ii). [abridged]

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