2004ApJ...605L.113L

Tycho's supernova remnant (SNR), as one of the few historical SNRs, has been widely studied in various wave bands. Observations show evidence that Tycho is expanding in a medium with density gradient and possibly interacting with a dense ambient medium toward the northeast direction. From the FCRAO CO survey of the outer Galaxy, we have identified a patch of molecular clouds in this area and have conducted a follow-up observation with the Nobeyama 45 m radio telescope. The high-resolution (16") Nobeyama data show that a large molecular cloud surrounds the SNR along the northeastern boundary. We suggest that Tycho's SNR and the molecular cloud are located in the Perseus arm and that the dense medium interacting with the SNR is possibly the molecular cloud. We also discuss the possible connection between the molecular cloud and the Balmer-dominated optical filaments and suggest that the preshock gas may be accelerated within the cosmic-ray and/or fast neutral precursor.