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Discovery of Molecular Shells Associated with Supernova Remnants. I. Kesteven 69

Supernova remnant (SNR) Kes 69 is morphologically characterized by brightened radio, infrared, and X-ray emission on the southeastern rim, with the 1720 MHz OH masers detected in the northeastern and southeastern regions at various local standard rest (LSR) velocities. We have performed a millimeter observation in CO and HCO+ lines toward \snr. From the northeastern compact maser region, 12CO and 13CO emission's peaks around 65 km/s and 85 km/s, which are consistent with the masers' LSR velocities, are detected. In the southeast, a molecular (12CO) arc is revealed at 77--86 km/s, well coincident with the partial SNR shell detected in the radio continuum and mid-infrared observations. An 85 km/s HCO+ emission is found to arise from a radio peak on the shell. Both the molecular arc and the HCO+ emission at ~85 km/s seem to be consistent with the presence of extended OH masers along the southeastern boundary of Kes 69. The morphology correspondence between the CO arc and other band emission of the Kes 69 shell provides strong evidence for the association between SNR Kes 69 and the ~85 km/s component of molecular gas. The multiwavelength emissions along the southeastern shell can be accounted for by the impact of the SNR shock on a dense, clumpy patch of molecular gas. This pre-existing gas is likely to be a part of the cooled debris of the material swept up by the progenitor's stellar wind. The association of SNR Kes 69 with the molecular cloud at the systemic velocity of ~85 km/s enables us to place the SNR at a kinematic distance of 5.2 kpc.