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Supernova remnant (SNR) G106.3+2.7 was recently found to be one of the fewpotential Galactic hadronic PeVatrons. Aiming to test how solid the SNR isassociated with the molecular clouds (MCs) that are thought to be responsiblefor hadronic interaction, we performed a new CO observation with the IRAM 30mtelescope toward its "belly" region, which is coincident with the centroid ofthe $\gamma$-ray emission. There is a filament structure in thelocal-standard-of-rest velocity interval $-8$ to $-5$ km/s that nicely followsthe northern radio boundary of the SNR. We have seen asymmetric broad profilesof $^{12}$CO lines, with widths of a few km/s along the northern boundary andin the "belly" region of G106.3+2.7, but similar $^{12}$CO line profiles arealso found outside the SNR boundary. Further, the low $^{12}$CO J=2-1/J=1-0line ratios suggest the MCs are cool. Therefore, it is still uncertain whetherthe MCs are directly disturbed by the SNR shocks, but we do find some cluesthat the MCs are nearby and thus can still be illuminated by the escapedprotons from the SNR. Notably, we find an expanding molecular structure with avelocity of $\sim$3.5 km/s and a velocity gradient of the MCs across the SNRfrom $\sim -3$ to $-7$ km/s, which could be explained as the effect of the windblown by the SNR's progenitor star.

IRAM 30 m CO-line Observation toward PeVatron Candidate G106.3+2.7: Direct Interaction between the Shock and the Molecular Cloud Remains Uncertain