Quantifying the Smoothness of the Stellar Halo: A Link to Accretion
  History
  We investigate the utility of the 3-dimensional Two-Point Correlation
Function (3D 2PCF) in quantifying substructure in the stellar halo of the Milky
Way, particularly as a means of constraining the accretion history of our
Galaxy. We use RR Lyrae variable stars from two different surveys as tracers of
the structure in the Galactic stellar halo. We compare our measurements of the
3D 2PCF in these datasets to a suite of simulations of the formation of the
stellar halo from Bullock and Johnston (2005). While there is some room for
interpretation, we find that the amounts of structure to be broadly consistent
with the simulations, while appearing smoother than average within the inner
halo and at small scales. This suggests a preferred accretion history scenario
in which the Milky Way's stellar halo acquired most of its mass about ~8
Gigayears ago, and has been largely quiescent since. Finally, we discuss the
prospects of statistical tools such as the 2PCF in the Gaia era of galactic
archaeology.
