Simulated ALMA observations of PONOS, performed using CASA. The field of view of the input image includes the main disc, and mergers A and B. Note that the output CASA mocks are flipped and rotated by 180 deg with respect to the maps shown in Figs. 11 and 12: in these mocks, merger A is to the north and the accreting filament to the south, while the main galaxy disc is still to the left (east) and merger B to the right (west). Upper left: ALMA mock map of the total [CI](2−1) line emission, at an observed frequency of 107.91 GHz (Band 5). The simulation uses the ALMA C-5 array configuration (0.30″ angular resolution, 3.62″ maximum recoverable scale (MRS)). Upper middle: total [CII] line mock map, at an observed frequency of 253.40 GHz (Band 6). The simulation uses the ALMA C-5 array configuration (0.24″ angular resolution, 2.91″ MRS). Upper right: total [OIII] line mock map, at an observed frequency of 460 GHz (Band 8). The simulation uses the ALMA C-3 array configuration (0.31″ angular resolution, 3.51″ MRS). Bottom panels: show the corresponding [CII] and [OIII] mocks obtained for the CGM component only (see Fig. 12). In all CASA simulations, the total integration time was set equal to 10 h (without overheads), and we simulated one velocity channel of 50 km s⁻¹ centred at v = 0 km s⁻¹.