As per Fig. 6 but showing the expected flux density of the [C i] emission based upon S_CO ≈ 2 × S _[C   i]  (Fig. 5). The dotted, broken and full traces show the rms sensitivity of the full ALMA array per each 1, 10 and 50 km  s^-1 channel for the conditions used above (10 h on source at a declination of δ = −30° and a vapour column density of 1.262 mm). The lower redshift trace spans the range given by the band-7, 6, 5 and 4 receivers (370−125 GHz) and the higher redshift spans that given by the band-3 and 2 receivers (116−67 GHz). The frequency scale is derived for the redshift of the [C i] transition. The stars show the known high redshifted [C i] emitters with the dotted line showing the least-squares fit to these.