Simulating star clusters across cosmic time – I. Initial mass function, star formation rates, and efficiencies
Year: 2019
Type: article
Abstract: 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 ($\overline{n}_{\rm gas} \sim 1.8\times 10^2$ 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 $40{{\ \rm per\ cent}}$ of the mass of the sink particle, while the remaining $60{{\ \rm per\ cent}}$ 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 ${\rm d}\rho _*/{\rm d}t \propto \rho _{\rm gas}^{1.5}$ if $\overline{n}_{\rm gas}\lt n_{\rm cri}\approx 10^3$ cm−3, and ${\rm d}\rho _*/{\rm d}t \propto \rho _{\rm gas}^{2.5}$ 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 $f_*=2{{\ \rm per\ cent}} (m_{\rm gas}/10^4~\mathrm{M}_\odot)^{0.4}(1+\overline{n}_{\rm gas}/n_{\rm cri})^{0.91}$, 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.
Authors: Chong-Chong He, Massimo Ricotti, Sam Geen
Institutions: University of Maryland, College Park, Heidelberg University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Awards: G1318933727, G63770550, A KEY GOAL OF COSMOLOGY IS TO UNDERSTAND THE ORIGIN AND EVOLUTION OF NONLINEAR STRUCTURE IN THE UNIVERSE INCLUDING STARS GALAXIES AND BLACK HOLES. RICH NEW SETS OF DATA WILL BECOME AVAILABLE SOON FROM MISSIONS SUCH AS JWST WFIRST X-RAY SURVEYOR ATHENA AND LISA AND WILL ADD TO OUR BREADTH OF INFORMATION ABOUT THIS CRITICAL EPOCH. ALTHOUGH CONSIDERABLE EFFORT HAS BEEN DEVOTED TO LARGE-SCALE COSMOLOGICAL SIMULATIONS WITH THE GOAL OF PROVIDING THEORETICAL GUIDANCE FOR THESE UPCOMING MISSIONS LESS ATTENTION HAS BEEN PAID TO THE EQUALLY IMPORTANT SMALLER-SCALE ASTROPHYSICAL PROCESSES THAT UNDERLIE THESE SIMULATIONS AND ARE BELOW THE RESOLUTION LIMIT OF MOST COSMOLOGICAL SIMULATIONS. WE PROPOSE TO EXPLORE SEVERAL ASPECTS OF THIS UNDERLYING ASTROPHYSICS RELATED TO COMPACT STAR CLUSTERS AT HIGH REDSHIFTS INCLUDING (1) THEIR ROLE IN THE PRODUCTION OF SEEDS FOR SUPERMASSIVE BLACK HOLES (SMBHS) (2) THE PHYSICS OF THEIR FORMATION AND GROWTH INCLUDING SUPER-EDDINGTON ACCRETION AND CLOUD FRAGMENTATION (3) THE ROLE OF X-RAY HEATING ON TRIGGERING COMPACT CLUSTERS FORMATION AND (4) THEIR EFFECT ON THE REIONIZATION OF THE UNIVERSE. WE WILL LINK OUR FINDINGS TO PREDICTION AND INTERPRETATION OF DATA FROM MISSIONS SUCH AS THOSE LISTED ABOVE. THIS WORK HAS DIRECT RELEVANCE TO STRATEGIC OBJECTIVE 1.6 OF NASA: DISCOVER HOW THE UNIVERSE WORKS EXPLORE HOW IT BEGAN AND EVOLVED AND SEARCH FOR LIFE ON PLANETS AROUND OTHER STARS. WITHIN THIS OBJECTIVE WE WILL INVESTIGATE THE NATURE OF BLACK HOLES AND THE PROCESSES OF FORMATION OF STARS AND GALAXIES.
OpenAlex ID: W2937479802