Dr. Pavel Mancera Piña (Leiden Observatory)
12 November 2025
11:30, Aula Piazzi
Abstract:
Gas-rich ultra-diffuse galaxies (UDGs) have the stellar mass of dwarfs but the effective radius and gas mass of massive spiral galaxies. The mechanisms of UDG formation have sparked intense debate in extragalactic astronomy, making it one of the most dynamic and contentious subjects in recent years. One of the main unanswered questions is whether their dark matter haloes are similar to those of other dwarf galaxies. The large neutral atomic gas (HI) reservoirs offer the opportunity to study their kinematics and constrain their dynamical and dark matter properties. I will present the results of an ongoing 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 derived from the decomposition of HI rotation curves imply that the dark haloes of these UDGs have structural parameters that differ from those expected in the CDM model. 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.