A large atomic hydrogen shell in the outer Galaxy: SNR or stellar wind bubble?
Abstract
We report the detection of a ring like HI structure toward l=90.0, b=2.8 with a velocity of vLSR=-99 km/s. This velocity implies a distance of d=13 kpc, corresponding to a Galactocentric radius of Rgal=15 kpc. The l-vLSR diagram implies an expansion velocity of vexp ~ 15 km/s for the shell. The structure has an oblate, irregular shell-like appearance which surrounds weak infrared emission as seen in the 60 micrometer IRAS data. At a distance of 13 kpc the size of the object is about 110 x 220 pc and placed 500 pc above the Galactic plane with a mass of 1e5 solar mass. An expanding shell with such a high mass and diameter cannot be explained by a single supernova explosion or by a single stellar wind bubble. We interpret the structure as a relic of a distant stellar activity region powered by the joint action of strong stellar winds from early type stars and supernova explosions.
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