ON THE NATURE OF 21 CM EMISSION PROFILE STRUCTURE AT HIGH GALACTIC LATITUDE - IMPLICATIONS FOR THE WARM NEUTRAL MEDIUM

Gaussian analysis of neutral hydrogen emission profiles obtained with the Arecibo 309 m, the NRAO 140 ft, and the Hat Creek 25 m radio teles copes reveal three distinct linewidth regimes. Component 1 is typicall y from 25-50 km/s wide and may be due to Galactic emission in far side lobes, although this remains to be proven. The bulk of this study conc erns Component 2, a pervasive feature approximately 12 km/s wide (full width at half maximum brightness), although somewhat narrower toward the North Polar Spur. If this component is due to a warm neutral mediu m, its linewidth implies a temperature of approximately 3000 K, substa ntially lower than many of the canonical values for this medium in the literature. On the other hand, there is evidence to suggest that at l east some of this component may be due to the superposition of unresol ved cool features in the beam. Component 3 encompasses narrow features with linewidths in the 2-6 km s-1 range with the majority around 3 km s-1.