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H-alpha from High Velocity Clouds

S. L. Tufte·R. J. Reynolds·L. M. Haffner
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Abstract

Optical emission lines provide an important new window on the HVCs. Recent studies of the H-alpha line reveal that ionized gas 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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BibTeXRIS

S. L. Tufte, R. J. Reynolds, L. M. Haffner. 1998-11-17. H-alpha from High Velocity Clouds. https://arxiv.org/abs/astro-ph/9811270

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