Distance Constraints for High Velocity Clouds from Optical Emission Lines

Details Distance Constraints for High Velocity Clouds from Optical Emission Lines Distance Constraints for High Velocity Clouds from Optical Emission Lines

2000-08-17

arxiv.org/abs/astro-ph/0008263v1

Astronomy and Astrophysics

Astrophysics

To appear in proceedings of Gas and Galaxy Evolution, (VLA 20th Anniversary Conference), ASP Conf. Series, ed. J. Hibbard, M.

Scientific paper

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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