Submillimeter/millimeter observations of the molecular clouds associated with Tycho's supernova remnant

We have carried out CO J = 2 − 1 and CO J = 3 − 2 observations toward Tycho's supernova remnant (SNR) using the KOSMA 3m-telescope. From these observations, we identified three molecular clouds (MCs) around the SNR. The small cloud in the southwest was discovered for the first time. In the north and east, two MCs (Cloud A and Cloud B) adjacent in space display a bow-shaped morphology, and have broad emission lines, which provide some direct evidences of the SNR-MCs interaction. The MCs are revealed at −69∼ −59 km s⁻¹, coincident with Tycho's SNR. The MCs associated with Tycho's SNR have a mass of ∼ 2.13 × 10³ M_⊙. Position-velocity diagrams show the two clouds to be adjacent in velocity, which means cloud-cloud collision could occur in this region. The maximum value (0.66 ± 0.10) of the integrated CO line intensity ratio (I_{CO J=3−2}/I_{CO J=2−1}) for the three MCs agrees well with the previous measurement of individual Galactic MCs, implying that the SNR shock drove into the MCs. The two MCs have a line intensity ratio gradient. The distribution of the ratio appears to indicate that the shock propagates from the southwest to the northeast.