2001ApJ...548..249K

Observations show significant Hα emissions in the Galactic halo near the edges of cold gas clouds of the Magellanic Stream. The source of the ionization of the cold gas is still a wide-open question. In our paper we discuss the critical velocity effect as a possible explanation for the observed Hα emission. The critical velocity effect can yield a fast ionization of cold gas if this neutral gas passes through a magnetized plasma under suitable conditions. We show that for parameters that are typical for the Magellanic Stream, the critical velocity effect has to be considered as a possible ionization source of high relevance.