of the disc. To demonstrate this, Fig. \[fig:disc\_recognition\_eda1c\] shows the difference between these two methods (dotted black line), the mass of ISM in the volume as determined with the Hop algorithm (green dashed line) and assuming the volume is completely filled with ISM (solid green horizontal line). In the beginning of the simulation, when the disc is stripped of its outer parts by the ram pressure exerted by the flow, the algorithm has some difficulties differentiating the disc from the ISM flow, but as soon as a stable situation is reached and the stripped outer edges of the disc have left the computational domain, it performs very well. The few spikes visible in Fig. \[fig:disc\_recognition\_eda1\] are artefacts: some particles are marked as part of the disc, while they are either being stripped from the outer edge (and already carry some angular momentum) or flow along the outer edge of the disc (and pick up some angular momentum from the disc). These artefacts do not influence our results as they are smoothed out when we linearly fit the data from the moment a steady state is reached.

Once we have determined which particles belong to the disc, we can also determine 