Mass estimators for flattened dispersion-supported galaxies
  We investigate the reliability of mass estimators based on the observable
velocity dispersion and half-light radius $R_\mathrm{h}$ for
dispersion-supported galaxies. We show how to extend them to flattened systems
and provide simple formulae for the mass within an ellipsoid under the
assumption the dark matter density and the stellar density are stratified on
the same self-similar ellipsoids. We demonstrate explicitly that the spherical
mass estimators (Walker et al. 2009, Wolf et al. 2010) give accurate values for
the mass within the half-light ellipsoid, provided $R_\mathrm{h}$ is replaced
by its `circularized' analogue $R_\mathrm{h}\sqrt{1-\epsilon}$. We provide a
mathematical justification for this surprisingly simple and effective
workaround. It means, for example, that the mass-to-light ratios are valid not
just when the light and dark matter are spherically distributed, but also when
they are flattened on ellipsoids of the same constant shape.
