Relations between physical subhalo properties (vertical axis) and observable proxies (horizontal axis). With black frames, we outline those finally used. Contours give the full distribution; we overplot the mean value of each subhalo property and its standard deviation for each bin in the observable (curves with error bars). Top left: age of the subhalo versus the projected radial separation of the subhalo from the main halo center. Top right: age of the subhalo versus redshift-corrected r − i. Middle left: age of the subhalo versus redshift-corrected u − r. See text for a description of the redshift correction. Middle right: age of the subhalo versus our morphology estimator. Bottom left: M_SUBF versus absolute r band magnitude. Bottom right: M_inf versus stellar mass (using results from Wang et al. 2006). Note that the contour levels differ between the panels.