accretion onto protoplanetary discs: ram pressure, angular momentum transport, dynamical encounters and external photo-evaporation.

Ram pressure stripping {#sec:rampressure_eda1}
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As the protoplanetary disc moves through the ISM, it experiences ram pressure, $P_{\rm ram} = \rho_{\rm ISM} v_{\rm ISM}^2$. This drag force can truncate the disc, depending on the gravitational force of the disc that keeps the latter bound to the star. By equating the gravitational force per unit area, or ‘pressure’, $P_{\rm grav}=GM_*\Sigma(r)r^{-2}$, of the disc to $P_{\rm ram}$, we determine beyond which radius the ram pressure dominates and the disc is expected to be truncated. This truncation radius is given by: $$\label{eq:ramradius_eda1}
R_{\rm trunc} = \left(\frac{GM_*\Sigma_0 \mathbf{r_0^n}}{\rho_{\rm ISM} v_{\rm ISM}^2}\right)^{\frac{1}{n+2}}$$ with $M_*$ the mass of the star and we have assumed that the surface density profile of the disc can be written as $\Sigma(r)=\Sigma_0 (r/r_0)^{-n}$, where $r_0$ is an arbitrary but constant radius to which $\Sigma_0$ is scaled. After the material at radii larger than $R_{\rm trunc}$ has been stripped from the disc, we expect further evolution of the disc to be determined by the redistribution of angular momentum due to accretion and viscous evolution. The pressure in the mid-plane of the disc is at least one order of 