The Missing Satellite Problem in 3D
  It is widely believed that the large discrepancy between the observed number
of satellite galaxies and the predicted number of dark subhalos can be resolved
via a variety of baryonic effects which suppress star formation in low mass
halos.Supporting this hypothesis, numerous high resolution simulations with
star formation, and associated feedback have been shown to reproduce the
satellite luminosity function around Milky Way-mass simulated galaxies at
redshift zero. However, a more stringent test of these models is their ability
to simultaneously match the satellite luminosity functions of a range of host
halo masses and redshifts. In this work we measure the luminosity function of
faint (sub-Small Magellanic Cloud luminosity) satellites around hosts with
stellar masses 10.5$<\log_{10}$M$_*$/M$_\odot<11.5$ to an unprecedented
redshift of 1.5. This new measurement of the satellite luminosity function
provides powerful new constraining power; we compare these results with
predictions from four different simulations and show that although the models
perform similarly over-all, no one model reproduces the satellite luminosity
function reliably at all redshifts and host stellar masses. This result
highlights the continued need for improvement in understanding the fundamental
physics that governs satellite galaxy evolution.
