Rigging dark halos: why is hierarchical galaxy formation consistent with the inside-out build-up of thin discs?

Understand

State-of-the-art hydrodynamical simulations show that gas inflow through the virial sphere of dark matter halos is focused (i.e.

• has a preferred inflow direction), consistent (i.e.
• its orientation is steady in time) and amplified (i.e.
• the amplitude of its advected specific angular momentum increases with time).