Title: Evidence for universality in the initial planetesimal mass function,
Abstract: Planetesimals may form from the gravitational collapse of dense particle
clumps initiated by the streaming instability. We use simulations of
aerodynamically coupled gas-particle mixtures to investigate whether the
properties of planetesimals formed in this way depend upon the sizes of the
particles that participate in the instability. Based on three high resolution
simulations that span a range of dimensionless stopping time $6 \times 10^{-3}
\leq \tau \leq 2$ no statistically significant differences in the initial
planetesimal mass function are found. The mass functions are fit by a
power-law, ${\rm d}N / {\rm d}M_p \propto M_p^{-p}$, with $p=1.5-1.7$ and
errors of $\Delta p \approx 0.1$. Comparing the particle density fields prior
to collapse, we find that the high wavenumber power spectra are similarly
indistinguishable, though the large-scale geometry of structures induced via
the streaming instability is significantly different between all three cases.
We interpret the results as evidence for a near-universal slope to the mass
function, arising from the small-scale structure of streaming-induced
turbulence.