t − z relations for the ages estimated using the Knowles model. The structure of this figure is the same as that in Fig. 6. The grey contours represent the case with f_v factors included, to account for the possible underestimation of age uncertainties. The t − z samplings on the right panel refer to this case. The contours in purple represent the case where these factors were not taken into account. The sampling of the associated posterior for t − z is not represented on the right panel for this case.