Star formation rate (SFR) as a function of time normalized to the maximum of the observed SFR (SFR_o). The upper panel shows the radial distance of the N-body system to the origin of the reference system centered on the MW’s barycentre for the best-fitting orbit. The lower panel shows the star formation triggered by the pericentre passages and we report the profile of SFR as deduced in Rizzi et al. (2003). In the lower panel thin green and black lines refer to the gas and bound mass fraction normalized to the initial value ( on the right vertical axis).