On the dark matter content of ultra-diffuse galaxies

I compare the dark matter content within stellar half-mass radius expected in a ΛCDM-based galaxy formation model with existing observational estimates for the observed dwarf satellites of the Milky Way and ultra-diffuse galaxies (UDGs). The model reproduces the main properties and scaling relations of dwarf galaxies, in particular their stellar mass-size relation. I show that the model also reproduces the relation between the dark matter mass within the half-mass radius, Mdm(<r1/2), and stellar mass exhibited by the observed dwarf galaxies. The scatter in the Mdm(<r1/2)-M_ relation is driven primarily by the broad range of sizes of galaxies of a given stellar mass. I also show the Mdm(<r1/2) of UDGs are within the range expected in the model for their stellar mass, but they tend to lie above the median relation due to their large sizes. The upper limits on Mdm(<r1/2) for the dark matter deficient UDGs are also consistent with the range of dark matter masses expected in the model. The most dark matter-deficient galaxies of a given size correspond to halos with the smallest concentrations and the largest ratios of M_/M200c. Conversely, the most dark matter-dominated galaxies are hosted by the highest concentration halos with the smallest M_/M200c ratios. The model indicates that the scatter between Mdm(<r1/2) and M200c is large, which renders inference of the virial mass from Mdm(<r1/2) uncertain and dependent on specific assumptions about the halo mass profile. Results presented in this paper indicate that dark matter-deficient UDGs may represent a tail of the expected dark matter profiles, especially if the effect of feedback on these profiles is taken into account.