The Angular Momentum Problems in Disk Galaxy Formation

In the current paradigm of galaxy formation, disk galaxies are assumed to form by the cooling and condensation of baryons within dark matter halos. In this scenario, the angular momentum of baryons and its distribution play key roles, which govern the structures of disk galaxies. However, some difficulties about angular momentum emerged for both analytic or/and semi-analytic models and numerical simulation of disk galaxy formation. The main problems include the angular momentum catastrophe, mismatch of angular-momentum profiles and so on. A number of mechanisms and various models have been proposed in order to resolve these problems. In the present paper, we describe in detail two main categories of angular momentum problems in disk galaxy formation, and summarize the methods which could solve these problems.