Correlations between T_age and L_X, L_X/L_γ, and L_s. The solid lines are the best linear fits, which are log L_X = −(2.44 ± 0.59)log T_age + (44.23 ± 1.89), log L_X/L_γ = −(3.37 ± 0.29)log T_age + (12.47 ± 0.94), and log L_s = −(2.83 ± 0.53)log T_age + (45.37 ± 1.59); the correlation coefficients r = 0.72, 0.95, and 0.80; and the probability of the null hypothesis P_null = 7.81 × 10^-4,3.15 × 10^-9, and 7.22 × 10^-5. The dashed lines are the 2σ confidence bands for the sample.