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| Paper: |
Distance Constraints for High-Velocity Clouds from Optical Emission Lines |
| Volume: |
240, Gas and Galaxy Evolution: A Conference in Honor of the 20th Anniversary of the VLA |
| Page: |
515 |
| Authors: |
Weiner, B. J.; Vogel, S. N.; Williams, T. B. |
| Abstract: |
We report results from a survey of high-velocity clouds (HVCs) and the Magellanic Stream (MS) for faint, diffuse optical recombination emission lines. We detect Hα emission with surface brightness from 41 to 1680 mR from HVCs, and from <40 to 1360 mR in the MS. A simple model for the photo-ionizing radiation emergent from the Galaxy, normalized to the HVCs A and M with known distances, predicts distances from a few to 40 kpc, placing the faintest HVCs in the Galactic halo, too far away for a Galactic fountain. This model cannot explain the bright and spatially varying Hα in the Magellanic Stream, which requires another source of ionization. However, we do not find any HVCs super-faint in Hα even with another ionization source, we conclude that the detected HVCs are not more than 2-4 times the distance of the MS (100-200 kpc). |
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