WHAM observations of H alpha emission from high-velocity clouds in the M, A, and C complexes

The first observations of the recently completed Wisconsin H alpha Mapper ( WHAM) facility include a study of emission lines from high-velocity clouds in the M, A, and C complexes, with most of the observations on the M I clou d. We present results including clear detections of H alpha emission from a ll three complexes with intensities ranging from 0.06 to 0.20 R. In every o bserved direction where there is significant high-velocity H I gas seen in 21 cm emission, we have found associated ionized hydrogen emitting the H al pha line. The velocities of the H alpha and the 21 cm emissions are well co rrelated in every case except one, but the intensities are not correlated. There is some evidence that the ionized gas producing the H alpha emission envelopes the 21 cm-emitting neutral gas, but the H alpha "halo," if presen t, is not large. If the H alpha emission arises from the photoionization of the H I clouds, then the implied incident Lyman continuum flux F-LC at the location of the clouds ranges from 1.3 to 4.2 x 10(5) photons cm(-2) s(-1) . If, on the other hand, the ionization is due to a shock arising from the collision of the high-velocity gas with an ambient medium in the halo, then the density of the preshocked gas can be constrained. We have also detecte d the [S II] lambda 6716 line from the M I cloud and have evidence that the [S II] lambda 6716 to H alpha ratio varies with location on the cloud.