Testing Galaxy Formation Scenarios with a NewMass Estimator

摘要

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 MD in ACDM 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 I-band mass-to-light ratios γ_(1/2)~1 The γ_(1/2)~1 vs. half-light mass M_(1/2), relation for pressure-supported galaxies follows a U-shape, with a broad minimum near γ_(1/2)~1≈ 3 that spans dwarf elliptical galaxies to normal ellipticals, a steep rise to γ_(1/2)≈3200 for ultra-faint dSphs, and a more shallow rise to γ_(1/2)~1≈800 for galaxy cluster spheroids.