The Stellar Mass Spectrum from Non-Isothermal Gravoturbulent Fragmentation

By A. Jappsen, Ralf Klessen, R. Larson, Yue-xing Li, M.-M. Mac Low Astrophysikalisches Institut Potsdam, Yale University, New Haven, A. History, New York., Columbia University. 2004

253 citations recorded by the source corpus.

The thermodynamic state of star-forming gas determines its fragmentation behavior and thus plays a crucial role in determining the stellar initial mass function (IMF). We address the issue by studying the effects of a piecewise polytropic equation of state (EOS) on the formation of stellar clusters in turbulent, self-gravitating molecular clouds using three-dimensional, smoothed particle hydrodynamics simulations. In these simulations stars form via a process we call gravoturbulent fragmentation, i.e., gravitational fragmentation of turbulent gas. To approximate the results of published predictions of the thermal behavior of collapsing clouds, we increase the polytropic exponent γ from 0.7 to 1.1 at a critical density n c , which we estimated to be $2.5\times10^5\,\mathrm{cm^{-3}}$. The change of thermodynamic state at n c selects a characteristic mass scale for fragmentation M ch , which we relate to the peak of the observed IMF. A simple scaling argument based on the Jeans mass $M_\mathrm{J}$ at the critical density $n_\mathrm{c}$ leads to $M_{\mathrm{ch}}\propto n_{\mathrm{c}}^{-0.95}$. We perform simulations with $4.3\times10^4\,\mathrm{cm^{-3}} < n_{\mathrm{c}} < 4.3\times10^7\,\mathrm{cm^{-3}}$ to test this scaling argument. Our simulations qualitatively support this hypothesis, but we find a weaker density dependence of $M_{\mathrm{ch}} \propto n_{\mathrm{c}}^{-0.5\pm0.1}$. We also investigate the influence of additional environmental parameters on the IMF. We consider variations in the turbulent driving scheme, and consistently find $M_{\mathrm{J}}$ is decreasing with increasing $n_{\mathrm{c}}$. Our investigation generally supports the idea that the distribution of stellar masses depends mainly on the thermodynamic state of the star-forming gas. The thermodynamic state of interstellar gas is a result of the balance between heating and cooling processes, which in turn are determined by fundamental atomic and molecular physics and by chemical abundances. Given the abundances, the derivation of a characteristic stellar mass can thus be based on universal quantities and constants.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/e311f50160564d8e5671c0103fd0ddc29bcc51bf

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Citations in the corpus

Physical Processes in the Interstellar Medium (2014, background): “Not only does this mechanism set the peak mass, but it also appears to produce a power-law distribution of masses at the high-mass end comparable to the observed distribution (Jappsen et al., 2005).”
Comparing the statistics of interstellar turbulence in simulations and observations - Solenoidal versus compressive turbulence forcing (2009, background): “In a follow-up study, we will include self-gravity and sink particles (e.g., Bate et al. 1995; Krumholz et al. 2004; Jappsen et al. 2005) to study the influence of the different forcings on the mass distributions of sink particles.”
The importance of radiative feedback for the stellar initial mass function (2008, methodology): “Hydrodynamical simulations using an equation of state inspired by Larson’s models and varying it to give a different characteristic Jeans mass do produce corresponding changes in the characteristic mass of the IMF (Jappsen et al. 2005; Bonnell, Clarke & Bate 2006).”
Gravitational fragmentation and the formation of brown dwarfs in stellar clusters (2008, background): “The initial cooling part of the equation of state mimics the effects of line cooling and ensures that the Jeans mass at the point of fragmentation is appropriate for characteristic stellar mass (Larson 2005; Jappsen et al. 2005; Bonnell, Clarke & Bate 2006).”