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tokens: the literature. Gray symbols show Local Group dwarf galaxies from Kirby et al. ( 2013 ), and gray dashed and dotted lines represent the median and 16th and 84th percentiles of the metallicity distributions. Cyan dashed and dotted lines show the median and 16th and 84th percentiles of the metallicity distributions for various types of galaxies in Gallazzi et al. ( 2005 ). Green symbols show the stellar mass–metallicity relation for early-type galaxies binned in stellar mass (Conroy et al. 2014 ). Top right: relation between velocity dispersion and [Fe/H] for DF 44, compared with early-type galaxies binned in velocity dispersion (Conroy et al. 2014 ), and Local Group dwarf galaxies (Kirby et al. 2013 ). Bottom left: relation between metallicity and the logarithmic ratio of stellar mass to dynamical mass for DF 44, Local Group dwarf galaxies (Kirby et al. 2013 ) and early-type galaxies binned in velocity dispersion (Conroy et al. 2014 ). Previous work concluded that some UDGs, including DF 44, may live in more massive dark matter halos than would be expected for their luminosities (e.g., M vir > 10 11 M ⊙ , van Dokkum et al. 2016 ). In addition, it is well-known that the stellar properties of early-type galaxies are tightly related to their dynamical masses (e.g., Gallazzi et al. 2006 ; Graves et al. 2009 ). Therefore, we also look into the relation between their stellar properties and gravitational potential well depth. The top right panel of Figure 12 shows the relation between stellar velocity dispersion ( σ ) and metallicities. We compare DF 44 with dwarf galaxies (Kirby et al. 2013 ), massive early-type galaxies binned in velocity dispersion (Conroy et al. 2014 ). We also compare to 12 elliptical and S0 galaxies in the Coma cluster (Trager et al. 2008 ). Their iron abundances are calculated based on their metallicities and the enhanced element abundances ([Z/H] and [E/Fe]) in Trager et al. ( 2008 ) and Equation (3) in Trager et al. ( 2000 ). DF 44 stands out in this plot in the sense that it has lower metallicity for its σ compared to other galaxies. We also know that the stellar mass of DF 44 is unusually low for its σ and since it is the (massive) stars that produce metals, it is perhaps not surprising that DF 44 has low metallicity for its σ . We explore this point further in the bottom-left panel of Figure 12 , where we plot [Fe/H] as a function of the logarithmic ratio of stellar mass to dynamical mass. This ratio is proportional to the integrated star formation efficiency. In this diagram, one can imagine diagonal tracks where a galaxy in a given halo evolves along the track as it converts baryons into stars. Tracks associated with more massive halos will be offset vertically in this diagram, as a given integrated star formation efficiency (a given stellar-to-dynamical mass ratio) will result in a higher stellar metallicity for galaxies in deeper potential wells, as such systems will be able to retain a greater fraction of the