Latitude extent of diffuse ionization in the Galaxy

Observations of radio recombination lines (H157a) at A18 cm, from regions free of discrete radio sources, show the line emission to be confined to within of the galactic equator at 1" = 33 . This angle implies the largest values of the measured physical parameter 22/ 2 to be entirely within 70 pc of the plane. Such a distribution appears to be consistent with that expected from a thermal gas in hydrostatic pressure equilibrium with a temperature of approximately 3600 K.