Streaming instability of multiple particle species II -- Numerical convergence with increasing particle number

Abstract

The streaming instability provides an efficient way of overcoming the growth barriers in the initial stages of the planet formation process. Considering the realistic case of a particle size distribution, the dynamics of the system is altered compared to the outcome of single size models. In order to understand the outcome of the multi-species streaming instability in detail, we perform a large parameter study in terms of particle number, particle size distribution, particle size range, initial metallicity and initial particle scale height. We study vertically stratified systems and determine the metallicity threshold for filament formation. We compare these with a system where the initial particle distribution is unstratified and find that its evolution follows that of its stratified counterpart. We find that change in particle number does not result in significant variation in the efficiency and timing of filament formation. We also see that there is no clear trend for how varying the size distribution in combination with particle size range changes the outcome of the multi-species streaming instability. Finally, we find that an initial metallicity of $Z_{\rm{init}}=0.005$ and $Z_{\rm{init}}=0.01$ both result in similar critical metallicity values for the start of filament formation. Our results show that the inclusion of a particle size distribution into streaming instability simulations, while changing the dynamics as compared to mono-disperse systems, does not result in overall unfavorable conditions for solid growth. We attribute the sub-dominant role of multiple species to the high-density conditions in the midplane, conditions under which also linear stability analysis predict little difference between single and multiple species.