Keck spectroscopy of the coma cluster ultra-diffuse galaxy Y358: dynamical mass in a wider context

We examine ultra-diffuse galaxies (UDGs) and their relation to non-UDGs in mass-radius-luminosity space. begin by publishing Keck/KCWI spectroscopy for the Coma cluster UDG Y358, which we measure both a recessional velocity dispersion. Our confirms association with Y358's status as UDG. From our dispersion (19 $\pm$ 3 km s$^{-1}$) calculate dynamical mass within half-light radius provides evidence core dark matter halo. compare this mass, along those globular (GC)-rich/-poor UDGs literature, profiles isolated, gas-rich NIHAO/FIRE simulations. find GC-poor have masses similar UDGs, suggesting an evolutionary pathway may exist between two. Conversely, GC-rich too massive be easily explained evolution of UDGs. The simulated match However, once compared stellar -- halo space, FIRE/NIHAO do not either or at same mass. Finally, supplement data Y358 other that measured dispersions literature. sample wide range finding locus luminosity primary difference being larger radii.