The hydrodynamic stability of gaseous cosmic filaments

TL;DR

This paper derives a stability criterion for cosmic web shocks, showing that gas cooling leads to filament instability, which influences how filaments feed halos across different mass ranges and redshifts.

Contribution

It introduces a new stability criterion for virial shocks in cosmic filaments considering cooling effects, and predicts filament instability ranges impacting galaxy formation.

Findings

Filament instability occurs for masses between 10^{11}-10^{13} M_sun Mpc^{-1}.

Unstable filaments likely feed halos of 10^{10}-10^{13} M_sun at z=3.

Stable filaments can feed larger halos at lower redshifts.

Abstract

Virial shocks at edges of cosmic-web structures are a clear prediction of standard structure formation theories. We derive a criterion for the stability of the post-shock gas and of the virial shock itself in spherical, filamentary and planar infall geometries. When gas cooling is important, we find that shocks become unstable, and gas flows uninterrupted towards the center of the respective halo, filament or sheet. For filaments, we impose this criterion on self-similar infall solutions. We find that instability is expected for filament masses between $10^{11}-10^{13}M_\odot Mpc^{-1}.$ Using a simplified toy model, we then show that these filaments will likely feed halos with $10^{10}M_{\odot}\lesssim M_{halo}\lesssim 10^{13}M_{\odot}$ at redshift $z=3$, as well as $10^{12}M_{\odot}\lesssim M_{halo}\lesssim 10^{15}M_{\odot}$ at $z=0$. The instability will affect the survivability of the filaments as they penetrate gaseous halos in a non-trivial way. Additionally, smaller halos accreting onto non-stable filaments will not be subject to ram-pressure inside the filaments. The instreaming gas will continue towards the center, and stop either once its angular momentum balances the gravitational attraction, or when its density becomes so high that it becomes self-shielded to radiation.