Extreme galaxies in fundamental scaling relations
I will discuss two of the most important scaling laws for disc galaxies: the baryonic Tully-Fisher relation (BTFR) and the specific angular momentum-mass relation. Specifically, I will focus on the location of rather extreme galaxy populations in such scaling laws. First, I will present recent results on the dynamics of gas-rich, extended low surface brightness galaxies, sometimes called ultra-diffuse galaxies (UDGs). Using a robust kinematic modelling fitting technique, we find that gas-rich UDGs are outliers of the BTFR and have baryon fractions as high as the cosmological average. Moreover, I will show that mass models of a gas-rich UDG pose a strong challenge to cold dark matter theories. In the second part of the talk, I will present new measurements of the stellar, gas, and baryonic specific angular momenta of disc galaxies, to then derive the relations between the specific angular momenta (j) and mass (M). I will report the discovery of empirical correlations between j, M, and the gas fraction fgas. These relations are very tight and are followed very well not only by normal galaxies but also by a set of extreme galaxies that are outliers of other scaling relations. Moreover, our scaling laws provide a direct benchmark to test the outcome and predictions of simulations and models.