Position of Tuc III relative to dwarf galaxy scaling relations. (upper left) Distribution of Milky Way globular clusters (small filled black points) and spectroscopically confirmed Milky Way satellite galaxies (open blue circles) in the plane of elliptical half-light radius and absolute magnitude. Tuc III is plotted as a filled red circle. (upper right) Dynamical mass-to-light ratios for dwarf galaxies and globular clusters as a function of absolute magnitude. Masses shown are calculated as the mass within the elliptical half-light radius using the formula from Wolf et al. (2010). Symbols are as in the upper left panel, except that Tuc III and Segue 2 are plotted as upper limits. (lower left) The luminosity–metallicity relation for dwarf galaxies and lack thereof for globular clusters. Symbols are the same as in the upper left panel. (lower right) Metallicity dispersion as a function of metallicity for dwarf galaxies and globular clusters. Symbols are the same as in the upper left panel. The globular cluster data shown in this figure are taken from the 2010 edition of the Harris (1996) catalog, with the exception of the metallicity dispersions, which are from Willman & Strader (2012) and references therein. Half-light radii of the dwarf galaxies are taken from the 2015 September update of the McConnachie (2012) compilation, while velocity dispersions are taken from McConnachie (2012) for classical dSphs and otherwise from Simon & Geha (2007), Simon et al. (2011), Willman et al. (2011), Koposov et al. (2011, 2015b), Kirby et al. (2013a, 2015a, 2015b), Simon et al. (2015), Martin et al. (2016), Kim et al. (2016), Collins et al. (2017), Li et al. (2016b), and M. Geha et al. (2017, in preparation). Dwarf galaxy metallicities and metallicity dispersions are from Kirby et al. (2013b), the velocity dispersion references just listed, and Frebel et al. (2014), Brown et al. (2014), and Koch & Rich (2014).