AAS 203rd Meeting, January 2004
Session 76 HII Regions
Poster, Wednesday, January 7, 2004, 9:20am-6:30pm, Grand Hall

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[76.05] A Galactic chimney above the W47 HII region complex

J. M. Stil, R. Ouyed, A. R. Taylor (University of Calgary), J. M. Dickey (University of Minnesota)

We present new 21-cm HI ine and 21-cm continuum images from the VLA Galactic Plane Survey (VGPS; Taylor et al. 2002) of the Galactic star formation region W47 and the associated "worm" GW 38.0+1.6 (Heiles et al. 1996). A vertical HI filament on the high-longitude edge of the W47 region is reported, that forms the seamless high-latitude extension of a thermal radio continuum filament detected previously in the continuum survey of Reich et al. (1990). The filament is detected up to the VGPS survey boundary at latitude b=+1.2 degrees (200 pc at the distance of W47). The remarkable morphological correspondence of the HI and continuum emission between latitudes 0.3 degree and 0.7 degree suggests that that both continuum and HI emission originate from the same structure. At lower latitudes (closer to the W47 HII regions), only continuum is observed; at higher latitudes, only HI is observed. The gradual curvature of the filament is consistent with a Kompaneets (1960) model for an expanding bubble in an exponential atmosphere, with the W47 region as the source, and outlining the larger GW 38.0+1.6 area. The Galactic worm GW 38.0+1.6 may well be a chimney above the W47 HII region complex. Surprising is the large velocity difference between the HI filament at V_LSR = 0 km/s and published radio recombination line velocities between V_LSR = +40 km/s and V_LSR = +60 km/s for the W47 region. This implies a large velocity component perpendicular to the expansion velocity of the super bubble/chimney. We are investigating theoretical scenarios for this large velocity component via 3-D numerical simulations.

The VGPS is supported by a grant to ART from the Natural Sciences and Engineering Council of Canada.

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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.