Logarithm of the soft‐band (0.11–0.41 keV) X‐ray luminosity, ﹩L^{s}_{\mathrm{X}\,}﹩, vs. the logarithm of the blue optical luminosity, L_B, for all of the galaxies in the sample. The notation is identical to that in Fig. 1. The best‐fit power‐law relations are ﹩L^{s}_{\mathrm{X}\,}\propto L^{1.94\pm 0.17}_{B}﹩ (solid line) (whole sample) and ﹩L^{s}_{\mathrm{X}\,}\propto L^{1.75\pm 0.16}_{B}﹩ (dotted line) (group center galaxies excluded from sample).