New Problems for the Formation of Disk Galaxies

The standard picture for the formation of disk galaxies has come to face a number of problems related to angular momentum. Numerical simulations produce disks that are too small, and analytical models predict too much low angular momentum compared to observations. In addition, angular momentum distributions of proto-galaxies in numerical simulations reveal large mass fractions with negative specific angular momentum, which implies that the gas cannot conserve its detailed distribution of specific angular momentum when cooling to form the disk. This crumples one of the main pillars of our standard picture, and indicates that a new spin on the angular momentum acquisition of disk galaxies may be required.