An Infrared and Radio Study of the Galactic Worm GW46.4+5.5

Abstract

We have carried out high-resolution (~3') HI and CO line observations of GW46.4+5.5 and analyzed available IR and radio emission survey data. GW46.4+5.5 appears as a long filamentary structure extending vertically from the Galactic plane in both far-IR and radio continuum maps. The I_60/I_100 ratio in the worm is estimated to be 0.29+-0.05, which is significantly higher than the value for the solar neighborhood. The high ratio is consistent with a hypothesis that the dusts in the worms have been processed by interstellar shocks. The radio continuum emission from the worm has a spectral index of -0.47 and does not correlate with I_60. Thus, most of the radio continuum emission is likely to be nonthermal. Our HI observations show that the HI gas is clumpy. We detected two molecular clouds associated with the HI peaks. The molecular clouds do not appear to be gravitationally bound. Using the Leiden-Dwingeloo HI data, we identify an expanding HI supershell associated with GW46.4+5.5, which is a size of 14^o*22^o. The supershell appears between 18 and 40 km/s, and decreases slowly in size as the velocity increases. An averaged l-v diagram reveals that the supershell has a central velocity of ~18 km/s (d_kin=1.4 kpc) and an expansion velocity of ~15 km/s. The structure is also visible in adio continuum maps. The observed molecular clouds might have condensed out of shock-compressed gas in GW46.4+5.5 because they are closely associated with the HI 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 the high-altitude clouds. Our results suggest that at least some of the high-altitude clouds might have formed in Galactic worms (or HI supershells).