Galactic disc formation from cold fractal gas

Abstract

It is likely that cold molecular clouds formed early, even before galaxies. In this work, we try to assess the consequences of using cold fractal gas for disc formation instead of hot gas, with a focus on angular momentum loss through dynamical friction. Using numerical simulations, we show that the dynamical friction from the dark matter halo on the cold gas fractal structures is not affected by the morphology of the structures, but is affected by their dynamical nature: their deformations and fluctuations. We argue that for typical values of the physical parameters during disc formation, the friction at small scale is reduced.