Abstract :
Ultra-diffuse galaxies (UDGs) have stellar masses of dwarf galaxies but effective radii comparable to massive spiral galaxies. The formation mechanisms of UDGs have sparked intense debate in extragalactic astronomy, marking it as one of the most dynamic and debated subjects in recent years. One of the main unanswered questions is whether their dark matter haloes are similar to those of other dwarf galaxies. A subset of the UDG population has large neutral atomic gas (HI) reservoirs, which opens up the possibility of studying their gas kinematics and constraining their dynamical properties.
I will present the results of a recent observational campaign obtaining ultra-deep HI and optical data on a sample of isolated gas-rich UDGs. Robust kinematic modelling shows that the galaxies have very low circular speeds for their baryonic mass, making them the first known galaxy population to deviate from the baryonic Tully-Fisher relation and suggesting that these galaxies have a baryon fraction close to the cosmological average.
I will show that mass models obtained from the decomposition of the HI rotation curve imply that the dark haloes of these UDGs have different structural parameters from those seen in CDM cosmological simulations. Finally, I will present mass models in the context of self-interacting and fuzzy dark matter. I will discuss whether these theories better fit the dynamics of UDGs than CDM and show explicitly how we can use gas-rich UDGs to constrain the nature of dark matter itself.
