ACA CO(3−2) spectrum extracted from a polygonal region tracing the 2σ contours in Fig. 1 which maximises the S/N (=5). The spectral profile is, however, almost identical to the ACA spectra extracted using circular or elliptical apertures with r_aperture ≳ 15″ (Fig. A.3, bottom panel). The spectral rms is 2.7 mJy per Δv_channel = 160 km s⁻¹. The best-fit Gaussian parameters are as follows: v_cen = 200 ± 100 km s⁻¹, FWHM = 1000 ± 220 km s⁻¹, and S_peak = 8.1 ± 1.6 mJy. At the bottom, shifted vertically to facilitate a visual comparison, we show the ALMA CO(3−2) spectrum extracted from a 1″-radius circular aperture. The green dot-dashed line indicates the ALMA CO(3−2) line peak (ν_obs = 107.4 GHz, z_CO = 2.2197).