the surface density profile, $\Sigma(r)$, and radius, $R_{\rm disc}$, of the disc. In order to do so, we calculate the column density of the disc, viewing the disc face-on. We then bin the obtained 2-D surface density in concentric annuli, which gives us the surface density profile as a function of the radius. At $t=0$, we determine $\Sigma(100 {\rm AU})$, i.e. at the initial outer radius of the disc. At consecutive times, we recalculate the surface density profile and consider the radius at which $\Sigma(r)\big|_{t} =\Sigma(100 {\rm AU})\big|_{t=0}$ to be the radius of the disc at that moment in time. The snapshots of our reference model, shown in Fig. \[fig:snapshots\_eda1\], illustrate that this method performs very well if the simulation has reached a steady state. Furthermore, the radius determined in this way also agrees with the estimate of the truncation radius due to ram pressure stripping, Eq. \[eq:ramradius\_eda1\], as can be seen in Fig. \[fig:disc\_recognition\_eda1b\] where we have plotted both radii as a function of time. Much in the same way as we did for the disc radius, the truncation radius in Fig. \[fig:disc\_recognition\_eda1b\] is derived from the surface density profile at each moment in time.

Angular momentum conservation {#sec:am_conservation_eda1}
