The dynamical lineage of field ultra-diffuse galaxies

Abstract

Ultra-diffuse galaxies (UDGs) exhibit morphological similarities with other low-luminosity galaxies indicating a possible evolutionary connection. We investigate for common dynamical characteristics of isolated, HI-rich UDGs with other low luminosity field galaxies, namely the low surface brightness galaxies (LSBs) and the dwarf irregulars (dIrrs). From the galaxy scaling relation studies, we note that UDGs and LSBs constitute statistically different populations. However, for UDGs and dIrrs, the null hypotheses of these statistical tests cannot be rejected : stellar mass versus atomic hydrogen mass; stellar mass versus dynamical mass; and dark matter core density versus core radius mass scaling. Interestingly, the dynamical models suggest that UDGs, LSBs and dIrrs constitute different galaxy populations as reflected by their radial-to-vertical velocity dispersion, and the rotational velocity-to-total stellar velocity dispersion. Finally, we observe that the total HI and stellar mass mostly regulate the variance in the structural and kinematical data both for the UDGs and dIrrs, while the ratio of radial-to-vertical velocity dispersion, and the total HI mass dominate the same in LSBs. UDGs and LSBs represent statistically different galaxy populations with respect to their mass and structural properties. But the fact that their structural parameters follow the same distributions is not ruled out. However, UDGs, dIrrs and LSBs constitute very different populations as far as their kinematical parameters are concerned. Finally, we note that the variation in the structural and kinematical data of both the UDGs and the dIrrs is mostly accounted for by their stellar mass and HI mass, whereas for the LSBs, the same is explained by the ratio of the radial-to-vertical stellar dispersion followed by the HI mass. Thus we conclude that the UDGs and dIrrs to share common dynamical lineage.