(\[\] line in ALMA Band 8) were observed; ALESS 67.1 ($z=2.12$) and ALESS 122.1 ($z=2.02$) have the \[\] line in ALMA Band 9, and were not observed. The total time including calibration and overheads was 72 mins, with an on-source time of 11 mins per target. The array configuration consisted of 38 12-m antennas, with baselines extending up to 1400 m. The largest angular scale[^3] of the observations is $\sim$1.9 arcsec for both sources. The primary beam FWHM is 14.1 arcsec. Synthesized beam sizes and $\sigma_{rms}$ for the 160-$\mu$m continuum and the \[\] emission are listed in Table \[tab:targets+observed\]. The target elevation range was 66–73 deg for ALESS 49.1 and 67–76 deg for ALESS 57.1.

The frequency setup was configured in four spectral windows (SPWs) in Band 8. The individual SPWs were centered at 481.953, 483.183, 493.506, 495.386 GHz. Each SPW was split into 480 frequency channels 3.906 MHz wide, giving a total bandwidth of 1.875 GHz per SPW. The radio-velocity resolution was 2.42 km s$^{-1}$. Both the Stokes $XX$ and $YY$ parameters were observed.

The data were calibrated using the standard ALMA pipeline, with additional flagging necessary to remove atmospheric features (see Section \[subsec:imaging\]). All the visibility data processing 