Enhanced CO<i>J</i>= 2–1/<i>J</i>= 1–0 Ratio as a Marker of Supernova Remnant–Molecular Cloud Interactions: The Cases of W44 and IC 443

Abstract

We present results of CO J \ 21 line mapping of molecular clouds in the vicinity of the supernova remnants (SNRs) W44 and IC 443. Large areas spanning were observed with the 9@ beam of D1 .5 ] 2 the University of TokyoNobeyama Radio Observatory 60 cm Survey Telescope. We identied six giant molecular clouds (GMCs) with masses (0.33) ] 105 around W44. Three show evidence of inter-M _ action with the SNR. In particular, one exhibits a line wing emission and an abrupt velocity shift at the position at which the cloud overlaps with the SNR. The CO J \ 21/J \ 10 line intensity ratio signicantly exceeds unity (1.3) in the wing. In IC 443, a high-velocity line wing emission was detected in CO J \ 21 with our 9@ beam. The CO J \ 21/J \ 10 ratio is extremely high ([3) in the wing, which suggests that the emission comes from spatially extended optically thin (q D 0.1), dense [n(H 2 ) D 105 cm~3], and warm (D80 K) gas. W44 is established as a good example of an SNR interacting with GMCs, while IC 443 is in interaction with a low-mass dark cloud. The mass and kinetic energy of the shocked gas are, respectively, 1 ] 103