H-alpha from High Velocity Clouds
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.
Cite
@article{arxiv.astro-ph/9811270,
title = {H-alpha from High Velocity Clouds},
author = {S. L. Tufte and R. J. Reynolds and L. M. Haffner},
journal= {arXiv preprint arXiv:astro-ph/9811270},
year = {2007}
}
Comments
12 pages, 10 figures. To be published in the Proceedings of the Stromlo Workshop on High Velocity Clouds, eds. B. K. Gibson and M. E. Putnam (ASP Conf. Series)