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.Positionvelocity diagrams show the two clouds to be adjacent in velocity,which means cloudcloud collision could occur in this region.The maximum value(0.66 ± 0.10) of the integrated CO line intensity ratio(ICOJ=3-2/ICOJ=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.