Intergalactic filaments as isothermal gas cylinders

Abstract

Using a cosmological simulation at redshift 5, we find that the baryon-rich cores of intergalactic filaments extending outwards from galaxies commonly form isothermal gas cylinders in regions favourable to their formation. The central gas density is typically about 500 times the cosmic mean total density, and the temperature is typically 1–2 × 104 K, just above the Lyman α cooling floor. These findings argue that the hydrodynamic properties of the gas are more important than the dark matter in determining this structure. It is noteworthy that the temperature and ionization state of the gas completely determine a finite total mass per unit length of an isothermal cylinder. Our findings may have implications for understanding the ‘cold-mode’ mechanism of gas transport into galaxies.