Speaker
Description
We analyse the internal structure and dynamics of cosmic-web filaments connecting massive high-z haloes. Our analysis is based on a high-resolution AREPO cosmological simulation zooming-in on three Mpc-scale filaments feeding three massive haloes of ~10^{12} Msun at z~4, embedded in a large-scale sheet. Each filament is surrounded by a cylindrical accretion shock at a radius corresponding to the virial radius of the dark matter filament. The post-shock gas is in virial equilibrium within the potential well set by an isothermal dark-matter filament. The filament line-mass, the gas fraction within r_shock, and the virial temperature all match expectations from analytical models for filament properties as a function of halo-mass and redshift. The filament cross-section has three radial zones. In the outer "thermal" (T) zone inward gravity and ram-pressure forces are over-balanced by outward thermal pressure forces, decelerating the inflowing gas and expanding the shock outwards. In the intermediate "vortex" (V) zone the velocity field is dominated by a quadrupolar vortex structure due to offset inflow along the sheet through the post-shock gas. The outward force is dominated by centrifugal forces associated with these vortices, with additional contributions from global rotation and thermal pressure. Shear and turbulent forces associated with the vortices act inwards. The inner "stream" (S) zone is a dense isothermal core, T~3x10^4 K and nH~0.01 cm^{-3}, defining the cold streams that feed galaxies. The core is formed by an isobaric cooling flow and is associated with a decrease in outward forces, though exhibiting both inflows and outflows. Cosmic web filaments thus contain a complex multiphase "circumfilamentary medium" (CFM), which is very similar to the CGM in galaxy halos. Differences in the thermal pressure in the CFM and the CGM can lead to rapid fragmentation of cold streams penetrating the virial shocks surrounding massive halos during cosmic noon, potentially explaining the large observed areal covering fractions of cold gas in the outskirts of such halos.