The difficulty of determining the mass (of the stars, gas, dark matter)
in individual galaxies conditions the uncertainty
on the estimate of the corresponding mass-to-light ratio M / L.
Various tracers have been used to probe the radial mass profiles of
galaxies at scales from tens of kpc down to the inner parsec,
starting with HI,
ionised and molecular gas velocity curves (see Sofue & Rubin
[1]
and references therein), and including
velocity dispersions and stellar proper motions as revealed in the
Near-Infrared. High-resolution two-dimensional kinematic maps of the
ionised (H
) gas in
nearby galaxies are now routinely obtained
[2,
3],
and used to better constrain their central
mass distribution. A battery of new techniques has now been advocated as
valid means for mass determination at large scales, getting help from
globular clusters, planetary nebulae, satellite galaxies, or stellar
streams, X ray distribution, and even lensing systems. In this short
review, I illustrate a few of these techniques in turn.