sources where the extended \[\] component is not expected to contribute significantly.

![image](mocks_49_cii.png){width="8.0cm"} ![image](mocks_57_cii.png){width="8.0cm"}\
![image](mocks_49_fir.png){width="8.0cm"} ![image](mocks_57_fir.png){width="8.0cm"}\

\[CII\] spectra and kinematics {#subsec:spectra+kinematics}
------------------------------

Figure \[fig:moments+spectra\] presents the \[\] moment-one (intensity-weighted velocity) maps and the comparison of \[\]/CO(3-2) line profiles in ALESS 49.1 and 57.1. The moment-one maps reveal a clear velocity gradient across both ALESS 49.1 and 57.1. The spectra were extracted from the naturally-weighted channel maps, using an aperture 1 arcsec ($\sim$8 kpc) in radius for CO(3–2) and 0.5 arcsec ($\sim$4 kpc) in radius for \[\], given the compact size of the \[\] emission.

The \[\] line profile in ALESS 49.1 largely traces the CO (3–2) profile, exhibiting an increased brightness in the blue channels. In ALESS 49.1, we find a tentative (2.5–3$\sigma$) increase in the \[\]/CO(3–2) ratio between the centre ($\pm$200 km s$^{-1}$) and the wings ($\pm(200-600$) km s$^{-1}$) of the lines. This might be due to: (1) a significant fraction of the \[\] emission in the reddest and bluest channels being very extended and thus resolved out by our Band 8 imaging, or (2) a spatial variation in the gas conditions. The \[/CO(3–2) ratio in ALESS 57.1 is consistent with being constant across the full velocity range.

![image](fig_mom-1_spectra.png){width="16cm"}\

