Evolution of dust grain size distribution by shattering in the interstellar medium: robustness and uncertainty

TL;DR

This study investigates the robustness and uncertainties in theoretical models of dust grain shattering in the interstellar medium, identifying key parameters affecting grain size distribution predictions and assessing their sensitivities.

Contribution

It highlights the critical role of the critical pressure $P_1$ in determining shattering timescales and provides insights into the uncertainties and simplifications in modeling dust grain size evolution.

Findings

The critical pressure $P_1$ is key to predicting grain size distribution.

Uncertainties in fragment ejection fractions cause moderate variations in results.

Fragment size distribution slope less than 3.5 has minor effects on outcomes.

Abstract

Shattering of dust grains in the interstellar medium is a viable mechanism of small grain production in galaxies. We examine the robustness or uncertainty in the theoretical predictions of shattering. We identify $P_1$ (the critical pressure above which the deformation destroys the original lattice structures) as the most important quantity in determining the timescale of small grain production, and confirm that the same $P_1/t$ ($t$ is the duration of shattering) gives the same grain size distribution [$n(a)$, where $a$ is the grain radius] after shattering within a factor of 3. The uncertainty in the fraction of shocked material that is eventually ejected as fragments causes uncertainties in $n(a)$ by a factor of 1.3 and 1.6 for silicate and carbonaceous dust, respectively. The size distribution of shattered fragments have minor effects as long as the power index of the fragment size distribution is less than ~ 3.5, since the slope of grain size distribution $n(a)$ continuously change by shattering and becomes consistent with $n(a)\propto a^{-3.5}$. The grain velocities as a function of grain radius can have an imprint in the grain size distribution especially for carbonaceous dust. We also show that the formulation of shattering can be simplified without losing sufficient precision.