Paper:	H alpha from HVCs
Volume:	166, Stromlo Workshop on High-Velocity Clouds
Page:	231
Authors:	Tufte, Stephen L.; Reynolds, Ron J.; Haffner, L. Matt
Abstract:	Optical emission lines provide an important new window on the HVCs. Recent studies of the H alpha line reveal that ionized hydrogen is pervasively associated with the neutral hydrogen in HVCs. The Wisconsin H alpha Mapper (WHAM) instrument has so far detected H alpha from high-velocity clouds in the M, A, and C complexes. We find a close spatial correspondence between the neutral and ionized portions of the HVCs with some evidence that the ionized gas envelopes the neutral part of the clouds. The velocities of the H alpha and 21-cm detections are well correlated, but the intensities are not. If the clouds are photoionized, the H alpha intensity is a direct measure of the Lyman continuum flux in the Galactic halo. Forthcoming observations of the H alpha line in combination with other emission lines will give new insights into the high-velocity cloud phenomena and will also probe the physical conditions of their environment.

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