Free Electrons Outside Hii Regions

Abstract

This paper reviews the recent observational results on the electron distribution outside the Hiiregions. The mean electron density in the solar neighbourhood is of the order of 0.03 cm-3, and does not seem to vary very much between the Hiclouds and the intercloud medium, or between the arms and the interarm region. The z thickness of the electron layer in the solar neighbourhood is found to be larger than or of the order of 0.8 kpc. No reliable figure of the electron distribution can be deduced for the moment in the inner parts of the Galaxy.