Abstract
In massive galaxies, dark matter is only detectable in the outer parts, in the form of a dark halo. The best tracer for the outer parts is the HI-21cm atomic gas, which traces the total mass. Inner galaxies, high-spatial-resolution ionized gas lines (Halpha, NII) and the CO line, a molecular gas tracer, reveal a constant density with radius in low-mass galaxies, rather than a cusp as predicted by the standard CDM model. Rotation curves depend mainly on the baryons ; there is a universal curve as a function of radius normalized to the effective radius. The baryonic Tully-Fisher scaling relation shows that baryons and dark matter are intimately coupled.
