¹²CO rotational temperatures (, computed by fitting a straight line to synthetic line intensities in the J_up = 5−10 range) obtained from isothermal non-LTE models. The red curve shows the parameter space that reproduces the observed T_rot of the HPVW component. The blue-shaded area shows the estimated gas density of the high-velocity cloudlets detected by ALMA (Goicoechea et al. 2018). The magenta, red, and blue curves show rms_min/rms contours of 1, 0.95, and 0.9 respectively, where rms refers to the rms value of log₁₀ (I_HIFI/I_mod).