Exploring the origin of gas-rich ultra-diffuse galaxies with HI kinematics

Ultra-diffuse galaxies (UDGs) are one of the most discussed topics in extra-Galactic astronomy in the last lustrum given their puzzling properties: they have luminosities typical of dwarf galaxies, but optical scale lengths similar to very massive spirals. This intriguing combination is hard to explain, and up to date the precise formation mechanism of UDGs remains unknown.

With the goal of learning more about their origins, our group has obtained resolved HI observations for a sample of gas-rich UDGs, and in this talk I will present some of our main results. By performing detailed kinematic modelling of our observations, we find that our UDGs show some startling properties: they are strong outliers of the baryonic Tully-Fisher relation (BTFR), they have a low dark matter content within the visible extent, and their baryon fraction is close to the cosmic average, meaning that our UDGs have virtually no"missing baryons". At the same time, there are hints suggesting that they may have a higher-than-average stellar specific angular momentum. In addition to this, I will present new evidence for a correlation between the offset from the BTFR and the optical disc scale length at low rotation velocities. I will discuss a possible formation mechanism associated with weak feedback processes, which may potential explain some of the observed properties in our UDGs.