Scaling and line types as in Fig. 13 but only accounting for old stars (>6 Gyr). This age cut-off is chosen to represent the stellar population that existed before the quenching of star formation in the two passage model (sex156-2). Hence the panels labeled “Isolation”, “One passage” and “Two passages” panels display the same stellar populations (the three-passage model [sex156-3] was quenched before this cut-off; however, with its massive disruption any gradient would be destroyed).