  The observed rotation curves of disc galaxies, ranging from late-type dwarf
galaxies to early-type spirals, can be fit remarkably well simply by scaling up
the contributions of the stellar and HI discs. This `baryonic scaling model'
can explain the full breadth of observed rotation curves with only two free
parameters. For a small fraction of galaxies, in particular early-type spiral
galaxies, HI scaling appears to fail in the outer parts, possibly due to
observational effects or ionization of the HI. The overall success of the
baryonic scaling model suggests that the well-known global coupling between the
baryonic mass of a galaxy and its rotation velocity (known as the baryonic
Tully-Fisher relation), applies at a more local level as well, and it seems to
imply a link between the baryonic mass distribution and the distribution of
total mass (including dark matter).
