Velocity-integrated ¹²CO intensity (W_CO) of two molecular clouds spatially coincident with the direction of LHAASO J2108+5157. Left: Integrated velocity of the first Gaussian component peaking at v₁ ≈ −11.8 km s⁻¹, with corresponding distance of d₁ ≈ 3.1 kpc. Right: Integral of the second Gaussian component at v₂ ≈ −2.7 km s⁻¹ and d₁ ≈ 2.0 kpc. The white contour represents 1420 MHz continuum emission from the Canadian Galactic Plane Survey (Taylor et al. 2003). The position of LHAASO J2108+5157 is marked with a black cross, and 95% UL on its extension (0.26°) is indicated with a black circle (Cao et al. 2021a). Bilinear interpolation is used to smooth out the contributions from individual pixels.