Molecular line observations of IC 443 - the interaction of a molecular cloud and an interstellar shock

The supernova remnant IC 443 is colliding with several molecular clouds which are now situated close to the expanding rim. Observations of CO, 13CO, HCO+, and HCN at frequencies between 88 and 356 GHz have been obtained toward several of these molecular clouds to examine the effects of the strong shock with the neutral gas in the clouds. The spatial distributions of CO, HCN and HCO+ are found to be very similar, and well correlated with that of shocked molecular hydrogen. The molecular lines observed from this area are very broad, having line-widths of up to 90 km s-1. The effect of the shock has been to cause extensive fragmentation of the cloud into dynamically unstable systems of fragments having typical size scales of 0.1-0.3 pc. A spectral line survey between 84 and 104 GHz has been carried out, which includes a number of molecular species which have been chosen as diagnostics of shock chemistry. Modeling carried out for several molecular species shows that CO emission from the high-velocity gas is usually optically thin, but for other species, the lines may be optically thick and subthermally excited