Testing galaxy formation scenarios with a new mass estimator
  We present the recently derived Wolf et al. (2009) mass estimator, which is
applicable for spherical pressure-supported stellar systems spanning over ten
orders of magnitude in luminosity, as a tool to test galaxy formation theories.
We show that all of the Milky Way dwarf spheroidal galaxies (MW dSphs) are
consistent with having formed within a halo of mass approximately 3 x 10^9 Msun
in LCDM cosmology. The faintest MW dSphs seem to have formed in dark matter
halos that are at least as massive as those of the brightest MW dSphs, despite
the almost five orders of magnitude spread in luminosity. We expand our
analysis to the full range of observed pressure-supported stellar systems and
examine their half-light I-band mass-to-light ratios. The M/L vs. half-light
mass M_1/2 relation for pressure-supported galaxies follows a U-shape, with a
broad minimum near M/L ~ 3 that spans dwarf elliptical galaxies to normal
ellipticals, a steep rise to M/L ~ 3,200 for ultra-faint dSphs, and a more
shallow rise to M/L ~ 800 for galaxy cluster spheroids.
