Time evolution of the intercentre distance r, in units of the radius R_p of the primary halo, of a pair of Sb + Sc galaxies with mass ratio 3:1 and internal spin parameter λ = 0.04 colliding along a radial orbit. The initial orientation of the internal spin of the haloes is X90Y90 (see Table 2). Different solid curves show merger histories calculated using different definitions of the galactic cores: green shows the 5% fraction of the most closely bound luminous particles, black shows the 10% fraction, blue shows the 25% fraction, and coral the 50% fraction, while the red line shows the merger evolution as determined from the central SMBH. The intersection of these curves with the grey horizontal dotted line marks the onset of the merger. The plot shows that the final coalescence of the galaxies at t/τ_dyn ∼ 2.4 is better delineated when the galactic cores are defined using a moderate fraction, between 5 and 25%, of the most closely bound particles.