MWISP ¹²CO (1–0) velocity-integrated intensity image of Tycho’s SNR. The unit of the scale bar is K km s^-1. The emission is integrated between −68 and −57 km s^-1, and the contours start at 5σ and then increase in steps of 3σ (1σ ~ 0.8 K km s^-1). The yellow solid lines show the arc-like structures observed in the three surrounding clouds around the remnant. The three arcs could be connected by the dashed lines and fitted into one complete ellipse, outlining a large cavity around the remnant. The three white dashed lines are shown to guide the eye for the stream-like structures seen in the cavity. The red circle shows the size (8′ in diameter) and position of the shell-like structure produced by the shockwaves from the supernova explosion, which was detected in the previous X-ray observations toward Tycho’s SNR (e.g., Warren et al. 2005).