Why Outflows Have Low Angular Momentum

摘要

We outline why galactic outflows preferentially remove low angular momentum mate-rial, and show that this is a natural result when structure forms in a cold dark matter cosmology. The driving factors are the fact that the mean angular momentum of accreted material increases with time, the existence of an extended reservoir of low angular momentum gas which is not within star forming regions and hence not subjected to being directly blown out and the tendency for outflows to follow the path of least resistance which is perpendicular to the disk.