We prove the existence and stability of flat steady states of the
Vlasov-Poisson system, which in astrophysics are used as models of disk-like
galaxies. We follow the variational approach developed by Guo and Rein for this
type of problems and extend previous results of Rein. In particular, we employ
a reduction procedure which relates the stability problem for the
Vlasov-Poisson system to the analogous question for the Euler-Poisson system.Comment: 21 page