Initial mass function of planetesimals formed by the streaming instability

TL;DR

This study uses large-scale simulations to analyze how the initial mass distribution of planetesimals formed by streaming instability depends on simulation box size, revealing a consistent exponentially tapered power-law distribution.

Contribution

It provides the first large-box simulations showing that the planetesimal mass function follows an exponentially tapered power law, with characteristic mass scales linked to filament mass budgets.

Findings

Mass function fits an exponential cutoff power law better than a pure power law.

Characteristic mass correlates with filament mass budget.

Results are consistent across different box sizes and resolutions.

Abstract

The streaming instability is a mechanism to concentrate solid particles into overdense filaments that undergo gravitational collapse and form planetesimals. However, it remains unclear how the initial mass function of these planetesimals depends on the box dimensions of numerical simulations. To resolve this, we perform simulations of planetesimal formation with the largest box dimensions to date, allowing planetesimals to form simultaneously in multiple filaments that can only emerge within such large simulation boxes. In our simulations, planetesimals with sizes between 80 km and several hundred kilometers form. We find that a power law with a rather shallow exponential cutoff at the high-mass end represents the cumulative birth mass function better than an integrated power law. The steepness of the exponential cutoff is largely independent of box dimensions and resolution, while the exponent of the power law is not constrained at the resolutions we employ. Moreover, we find that the characteristic mass scale of the exponential cutoff correlates with the mass budget in each filament. Together with previous studies of high-resolution simulations with small box domains, our results therefore imply that the cumulative birth mass function of planetesimals is consistent with an exponentially tapered power law with a power-law exponent of approximately -1.6 and a steepness of the exponential cutoff in the range of 0.3-0.4.