Cake Talk by Pavel Mancera Piña - Kapteyn Astronomical Institute & ASTRON

Ultra-diffuse galaxies (UDGs) are a subset of the low surface brightness galaxies characterised by their large optical disc scale length. While the formation mechanisms of UDGs have been widely discussed in the literature, no clear picture has yet emerged. A way to investigate the nature of UDGs is through the exploration of their kinematic and dynamical properties. For this, gas-rich UDGs are extremely useful, since their large gas reservoirs allow us to trace their rotation velocities and thus their potential well out to large distances from their centres.

I will present recent results that our group has obtained regarding the HI-kinematics of gas-rich UDGs. First, I will discuss how several gas-rich UDGs shift off the baryonic Tully-Fisher relation. This deviation implies that these galaxies have a baryon fraction close to the cosmological average, suggesting a weak-feedback formation mechanism where most of their gas was not ejected out of their discs. Finally, I will show new VLA high-resolution observations of one of these UDGs. The new data confirm our previous findings and allow us to perform the rotation curve decomposition of the galaxy, which seems to pose a strong challenge to both CDM and MOND.