BondiHoyleLittleton accretion and the uppermass stellar initial mass function
Abstract
We report on a series of numerical simulations of gas clouds with selfgravity forming sink particles, adopting an isothermal equation of state to isolate the effects of gravity from thermal physics on the resulting sink mass distributions. Simulations starting with supersonic velocity fluctuations develop sink mass functions with a highmass powerlaw tail dN/d log M ∝ M^{Γ}, Γ = 1 ± 0.1, independent of the initial Mach number of the velocity field. Similar results but with weaker statistical significance hold for a simulation starting with initial density fluctuations. This mass function powerlaw dependence agrees with the asymptotic limit found by Zinnecker assuming BondiHoyleLittleton (BHL) accretion, even though the mass accretion rates of individual sinks show significant departures from the predicted dot{M}∝ M^2 behaviour. While BHL accretion is not strictly applicable due to the complexity of the environment, we argue that the final mass functions are the result of a relative M^{2} dependence resulting from gravitationally focused accretion. Our simulations may show the powerlaw mass function particularly clearly compared with others because our adoption of an isothermal equation of state limits the effects of thermal physics in producing a broad initial fragmentation spectrum; Γ → 1 is an asymptotic limit found only when sink masses grow well beyond their initial values. While we have purposely eliminated many additional physical processes (radiative transfer, feedback) which can affect the stellar mass function, our results emphasize the importance of gravitational focusing for massive star formation.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 September 2015
 DOI:
 10.1093/mnras/stv1285
 arXiv:
 arXiv:1506.02591
 Bibcode:
 2015MNRAS.452..566B
 Keywords:

 stars: formation;
 stars: luminosity function;
 mass function;
 ISM: clouds;
 Astrophysics  Astrophysics of Galaxies
 EPrint:
 Accepted by MNRAS. 10 pages, 14 figures