Comparison of the o-H₂D⁺(1_1,0−1_1,1) spectra observed by APEX (red) and ALMA (black) in AG351 and AG354, from left to right. For a fair comparison, the APEX spectra from Sabatini et al. (2020) were converted in flux units using the APEX gain (40 Jy K⁻¹). The ALMA spectra were computed integrating the signal over an area corresponding to the APEX beam size (16.8″), and they were smoothed to the APEX spectral resolution.