The dynamical lineage of ultra-diffuse galaxies from TNG50-1

Abstract: The formation and evolution of the ultra-diffuse galaxies (UDGs) continues to remain a puzzle. Similarities and differences in the morphological and the kinematical properties of the UDGs with their possible precursors, namely low-surface brightness (LSBs), L*-type high-surface brightness (HSBs) and dwarf galaxies, may provide crucial constraints on their origin and evolution. We selected samples of UDGs, LSBs, HSBs and dwarfs from TNG50-1. We first obtained a few possible scaling relations involving some mass properties to analyse if the regression fits for UDGs are in compliance with those of the other samples. Then, we studied individual galaxy cutouts to evaluate the intrinsic shapes of their dark-matter (DM) and stellar components, orbital and kinematical properties related to their stellar velocity dispersion. Finally, we constructed the mock IFU data using the SimSpin code to extract the stellar kinematic moment maps. We observe that the UDGs and the dwarf galaxies have nearly similar regression fits in a. stellar-to-gas mass ratio vs gas mass, b. stellar-to-gas mass ratio vs total dynamical mass, c. stellar central surface density vs ratio of stellar-to-total dynamical mass, and d. total baryonic mass vs total dynamical mass parameter spaces. Next, we find that the isolated UDGs are prolate rotators similar to the dwarf population, while the tidally-bound UDGs can exhibit both prolate and oblate-rotating shapes. The DM and stellar velocity anisotropy properties of the UDGs suggest that they reside in a cored, dwarf-like halo and may be classified by early-type galaxies. Finally, the stellar kinematic properties suggest that both the UDGs and the dwarfs are slow-rotators having low to nearly no-rotations in contrast to the late-type, disc-dominated, fast-rotating LSBs and HSBs. Therefore, we may conclude that the UDGs and the dwarfs possibly have a common dynamical lineage.