An Infrared and Radio Study of the Galactic Worm GW 46.4+5.5

We have carried out high-resolution (~3') HI and CO line observations ofGW46.4+5.5 and analyzed available IR and radio emission survey data. GW46.4+5.5appears as a long filamentary structure extending vertically from the Galacticplane in both far-IR and radio continuum maps. The I_60/I_100 ratio in the wormis estimated to be 0.29+-0.05, which is significantly higher than the value forthe solar neighborhood. The high ratio is consistent with a hypothesis that thedusts in the worms have been processed by interstellar shocks. The radiocontinuum emission from the worm has a spectral index of -0.47 and does notcorrelate with I_60. Thus, most of the radio continuum emission is likely to benonthermal. Our HI observations show that the HI gas is clumpy. We detected twomolecular clouds associated with the HI peaks. The molecular clouds do notappear to be gravitationally bound. Using the Leiden-Dwingeloo HI data, weidentify an expanding HI supershell associated with GW46.4+5.5, which is a sizeof 14^o*22^o. The supershell appears between 18 and 40 km/s, and decreasesslowly in size as the velocity increases. An averaged l-v diagram reveals thatthe supershell has a central velocity of ~18 km/s (d_kin=1.4 kpc) and anexpansion velocity of ~15 km/s. The structure is also visible in adio continuummaps. The observed molecular clouds might have condensed out ofshock-compressed gas in GW46.4+5.5 because they are closely associated with theHI gas in velocity as well as in position. Their altitudes are 80 and 100 pc,respectively, and their physical properties are very similar to those of thehigh-altitude clouds. Our results suggest that at least some of thehigh-altitude clouds might have formed in Galactic worms (or HI supershells).Comment: 14 pages, 12 postscript figures, Accepted for publication in Ap