(a) Luminosity–metallicity relation. The dashed line shows the linear fit to the galaxies except Tri II (Kirby et al. 2013b, 2015c), and the dotted lines show the rms dispersion about the fit. (b) Masses of MW satellite galaxies within their 3D half-light radii assuming dynamical equilibrium. Data are from McConnachie (2012, and references therein), Simon et al. (2015), Koposov et al. (2015), and Kirby et al. (2015c). (c) Mass-to light ratios within the 3D half-light radii. (d) Mass densities within the 3D half-light radii.