A COMPARISON OF DIFFUSE IONIZED AND NEUTRAL HYDROGEN AWAY FROM THE GALACTIC PLANE - H-ALPHA-EMITTING H-I CLOUDS

We compare velocity-resolved maps of the interstellar H alpha emission at 1 degrees angular resolution within a 10 degrees x 12 degrees region of the sky, and 3' resolution within a 1 degrees x 1 degrees region, with corresponding maps of 21 cm emission. The results indicate that at least 30% of the H alpha background and 10%-30% of the 21 cm emission are spatially and kinematically associated with ''clouds'' containing both neutral and ionized hydrogen. These H alpha-emitting H I clouds, identified as prominent Her and 21 cm emission enhancements of several degrees extent on narrow (12 km s(-1)) velocity interval maps, have H I column densities that range from about 2 x 10(19) cm(-2) to 2 x 10(20) cm(-2) and emission measures from 2 cm(-6) pc to 10 cm(-6) pc. Their radial velocities suggest distances \z\ from the Galactic midplane that range from \z\ less than or similar to 100 pc to \z\ approximate to 1 kpc, with a \z\-distribution that is much thicker than that of the non-H alpha-emitting H I. The high \z\ H alpha-emitting H I clouds identified on these maps are approximately 40% ionized, have densities n approximate to 0.2-0.3 cm(-3), and are associated with large filament and loop structures. The relationship between the H degrees and the H+ within these clouds is not clear; however, the available data suggest that the neutral and ionized components of each cloud are spatially separated. If the clouds are photoionized, the H alpha surface brightnesses imply that at \z\ x 1 kpc the strength of the incident Lyman continuum flux 4 pi J approximate to 2 x 10(6) photons cm(-2) s(-1).