Title:The Nature(s) and Properties of the Ultra-Faint dSph Galaxies

Scientific program:
with M/L  10 &minus 100. Despite varying over three orders of magnitude in luminosity, all of these systems
have a minimum half-light radius of 100pc, and similar (dark) mass (107M) within their luminous regions.
This suggests that dSphs are the scale at which galaxy mass decouples from luminosity, with 107M being a
minimum mass for a luminous galaxy. This mass then tells us something fundamental either about dark matter
(different particle types correspond to different minimum halo masses), or about the conditions necessary for
galaxy formation, or both. The candidate ultra-faint dSphs discovered in the past three years from SDSS
extend the galaxy luminosity function faintward by an additional three orders of magnitude. These extreme
objects provide a unique opportunity to test models of galaxy formation. We propose a large programme with
VLT-FLAMES to observe all the stars with r  22 in all nine ultra-faint dSphs accessible by the VLT. These
observations will allow us to place the first reliable constraints on the kinematics and masses of the ultra-faint
dSphs, to determine any internal abundances spread, and to clarify the nature of the several ambiguous objects
- disrupted dSph or star cluster? - shedding light on the properties of the most extreme galaxies known.