A Gas Centric Model For Intergalactic Filament Development During the First Gigayear
Using a cosmological simulation of the first gigayear of the universe, we find that the mass per unit length of reionizing intergalactic filaments is proportional to the square of the sound speed with a proportionality constant equal to that predicted for a gravitationally bound, isothermal cylinder. These cylinders contain both gas and dark matter, and the dark matter contributes to the gravitational field roughly in proportion to its abundance. The dark matter of each galaxy collapses according to the cycloid predicted for spherically symmetric collapse in an expanding universe. In contrast, the gas collapses more slowly into the centre of the galaxy. After reionization filaments persist and, in some cases, become enriched in either gas or dark matter. We have incorporated these findings into a unified model. A key feature of a gravitationally bound, isothermal cylinder is that the mass per unit length depends only upon the temperature and ionization state of the gas. This property suggests a lower limit on the sizes of galaxies that can form from a filamentary precursor. The model may relate to outstanding problems in galaxy formation and reionization.