Mapping the core mass function to the initial mass function

Abstract

It has been shown that fragmentation within self-gravitating, turbulent molecular clouds ("turbulent fragmentation") can naturally explain the observed properties of protostellar cores, including the core mass function (CMF). Here, we extend recently-developed analytic models for turbulent fragmentation to follow the time-dependent hierarchical fragmentation of self-gravitating cores, until they reach effectively infinite density (and form stars). We show that turbulent fragmentation robustly predicts two key features of the IMF. First, a high-mass power-law scaling very close to the Salpeter slope, which is a generic consequence of the scale-free nature of turbulence and self-gravity. We predict the IMF slope (-2.3) is slightly steeper then the CMF slope (-2.1), owing to the slower collapse and easier fragmentation of large cores. Second, a turnover mass, which is set by a combination of the CMF turnover mass (a couple solar masses, determined by the `sonic scale' of galactic turbulence, and so weakly dependent on galaxy properties), and the equation of state (EOS). A "soft" EOS with polytropic index $\gamma <1.0$ predicts that the IMF slope becomes "shallow" below the sonic scale, but fails to produce the full turnover observed. An EOS which becomes "stiff" at sufficiently low surface densities ${\Sigma }_{\mathrm{gas}}\sim 5000M_{\odot }\mathrm{p}{\mathrm{c}}^{-2}$, and/or models where each collapsing core is able to heat and effectively stiffen the EOS of a modest mass ($\sim 0.02M_{\odot }$) of surrounding gas, are able to reproduce the observed turnover. Such features are likely a consequence of more detailed chemistry and radiative feedback.

13 pages, 15 figures, accepted by MNRAS on 17 April 2015

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