The baryonic Tully-Fisher relation and its implication for dark matter halos

Context. The baryonic Tully-Fisher relation (BTF) is a fundamental relation between baryonic mass and maximum rotation velocity. It can be used to estimate distances, as well as to constrain the properties of dark matter and its relation with the visible matter. Aims. In this paper, we explore if extremely low-mass dwarf galaxies follow the same BTF relation as high-mass galaxies. We quantify the scatter in the BTF relation and use this to constrain the allowed elongations of dark matter halo potentials. Methods. We obtained H i synthesis data of 11 dwarf galaxies and derive several independent estimates for the maximum rotation velocity. Results. Constructing a BTF relation using data from the literature for the high-mass end, and galaxies with detected rotation from our sample for the low-mass end results in a BTF with a scatter of 0.33 mag. Conclusions. This scatter constrains the ellipticities of the potentials in the plane of the disks of the galaxies to an upper limit of 0-0.06, indicating that dwarf galaxies are at most only mildly tri-axial. Our results indicate that the BTF relation is a fundamental relation which all rotationally dominated galaxies seem to follow.