Justin Read - January 23, 2015

The edge of galaxy formation

The LCDM cosmological model has been tremendously successful at explaining a host of
observational data on scales larger than ~1Mpc. However, on smaller scales there have
been two long standing puzzles: the cusp/core and missing satellites problems. While
many solutions have been suggested for both, it remains unclear whether the full
solution lies purely in "baryonic physics" or whether we must modify the cosmological
model on small scales. In this talk, I show how we can make progress by focussing on
the very smallest galaxies in the Universe. I present two new methods for weighing
these tiny galaxies, the former making use of tidal distortions at their edges; the
latter using ~4pc resolution simulations of isolated dwarfs (at which resolution, the
simulations become insensitive to details of the 'sub-grid' modelling). Armed with a
measure of the total mass, I show that either abundance matching below ~10^10 Msun
fails or we must indeed consider modifications to LCDM. The striking implication of the
former is that the Milky Way must be surrounded by many "dark dwarfs" that are more
massive than their visible counterparts.