2019MNRAS.484.2556L

We investigate the utility of the three-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 data sets 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 our measurements of substructure broadly consistent with the simulations: exhibiting significant substructure, but also appearing noticeably smoother than the majority of the simulated haloes. This suggests a preferred accretion history scenario in which the Milky Way's stellar halo acquired most of its mass about ∼9-10 Gyr 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.