High velocity HI is not associated with TeV supernova remnant W51C

Abstract

The recently-detected TeV gamma-ray source HESS J1923+141 coincides with Supernova Remnant (SNR) W51C and the star forming region W51B of the W51 complex. We construct HI absorption spectra to SNR W51C, HII regions G49.2-0.35 and G49.1-0.38 in W51B, and a nearby compact extragalactic source. Our study detects high-velocity (HV) HI clouds (above 83 km/s) which coincide with W51B, but finds that the clouds are behind W51B. Both W51C and G49.2-0.35 have have similar highest-velocity absorption features at ~70 km/s. The HII region G49.1-0.38 is behind the SNR because its HI absorption spectrum has a feature at 83 km/s. These new results argue against previous claims that the SNR has shocked the HV HI clouds. Therefore the TeV emission from the complex should not be associated with the HV HI clouds. W51C has a distance of about 4.3 kpc, smaller than the tangent point distance of 5.5 kpc in that direction, but still in the Sagittarius spiral arm.

6 pages, 4 figures, ApJ Letters, in press

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• Trigonometric Parallaxes of Massive Star Forming Regions: VI. Galactic Structure, Fundamental Parameters and Non-Circular Motions
• The VLA Galactic Plane Survey
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• Evolutionary Models for 15 Galactic Supernova Remnants with New Distances
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• Localized SiO emission triggered by the passage of the W51C SNR shock
• The Age Evolution of the Radio Morphology of Supernova Remnants
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• Evidence for particle acceleration approaching PeV energies in the W51 complex
• QUIJOTE scientific results -- V. The microwave intensity and polarisation spectra of the Galactic regions W49, W51 and IC443