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Distance Constraints for High Velocity Clouds from Optical Emission Lines

Benjamin J. Weiner·Stuart N. Vogel·T. B. Williams
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Abstract

We report results from a survey of high velocity clouds and the Magellanic Stream for faint, diffuse optical recombination emission lines. We detect H-alpha emission with surface brightness from 41 to 1680 milli-Rayleighs (mR) from HVCs, and from <40 to 1360 mR in the MS. A simple model for the photoionizing 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 H-alpha in the Magellanic Stream, which requires another source of ionization. However, we do not find any HVCs super-faint in H-alpha; 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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Benjamin J. Weiner, Stuart N. Vogel, T. B. Williams. 2000-08-17. Distance Constraints for High Velocity Clouds from Optical Emission Lines. https://arxiv.org/abs/astro-ph/0008263

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