from the centre of the source.

### \[CII\] emission

The velocity-integrated maps of the \[\] emission are presented in Figure \[fig:aless\_images\]. The \[\] emission is detected at 5- and 8$\sigma$ significance in ALESS 49.1 and 57.1, respectively. The \[\] emission is relatively compact ($<$0.5 arcsec diameter) in both ALESS 49.1 and 57.1, similar in extent to the 160-$\mu$m continuum. The \[\] emission in ALESS 57.1 is highly elliptical (axis ratio $\geq$2:1) and elongated in the east-west direction; the \[\] does not show any significant offset from the 160-$\mu$m peak. Note that the low-significance clumpy substructure such as that seen in ALESS 49.1 \[\] maps is often an artifact of low SNR (e.g.,@Hodge2016 [@Gullberg2018]), rather than a real physical feature.

![image](fig_ALESS_49_1_continuum_zoomed.png){height="4.5cm"} ![image](fig_aless49_cii.png){height="4.5cm"}

![image](fig_aless57_cont_zoom.png){height="4.5cm"} ![image](fig_aless57_cii.png){height="4.5cm"}\

*uv*-plane analysis {#subsec:uv-plane}
-------------------

We estimate the size of the continuum and \[\] emission regions by directly fitting the observed visibility function. Given the relatively low SNR of the data, we assume the surface brightness distribution to follow a circularly symmetric Gaussian profile.

The size is measured using the spectrally-averaged continuum and line datasets. To correct the offset between the phase-tracking centre and the centroid of the surface brightness distribution given in Table \[tab:targets+observed\], each dataset is 