Structure and kinematics of dense gas associated with the supernova remnant IC 443

We present the results of systematic, high-resolution J = 1 → 0 CO and HCO⁺ mapping observations of IC 443 carried out with the FCRAO 14 m radio telescope. Five new clumps of perturbed molecular gas have been identified and their relationship to one another clarified. Together with three previously known perturbed regions, the clumps outline a roughly elliptical ring whose major axis is ∼9 pc across. There is a surprisingly systematic variation in the distribution of the high-velocity molecular gas associated with the clumps, which suggests that the clumps are distributed along the periphery of a tilted, expanding ring. The clumpiness of this ring may be a byproduct of the supernova blast wave's interaction with a more homogeneous confining structure or the clumps may have existed prior to the supernova event; in that case, their distribution may reflect the distribution of pre-existing dense cores in the ambient molecular gas, whose geometry has been revealed by the supernova stripping off overlying cloud material. High-resolution 1.3 mm CO maps of several clumps were also made. The most prominent clump in the supernova remnant possesses a velocity field with a strong systematic component, which we interpret as an indication that some of the high-velocity gas is ablated clump material accelerated at a shock interface between the clump and hot, outflowing gas within the supernova cavity. Assuming all the shocked CO emission in the SNR to be optically thin (an assumption which receives some support from ¹³CO observations made toward the center of one clump), we estimate the total mass of molecular gas perturbed by the SNR to be at least 500 M_⊙. A similar estimate based on the HCO⁺ observations - an estimate which is unaffected by optical depth ambiguities and by the necessity of avoiding the spurious inclusion of quiescent foreground material in the mass estimate - yields a mass of ∼2000 M_⊙. Together with the expansion velocity of the clumps, ∼25 km s^-1, this leads to an expansion energy of ∼10⁴⁹ ergs, ∼5%-10% of the total estimated blast wave-energy of the supernova event. The large value of the total clump mass and the lower limit to the [¹²C/¹³C] isotope ratio suggested by our observations establish that the shocked gas associated with IC 443 represents preexisting molecular cloud material now interacting with the supernova remnant.