  The observed population of the Milky Way satellite galaxies offer a unique
testing ground for galaxy formation theory on small-scales. Our novel approach
was to investigate the clustering of the known Milky Way satellite galaxies and
to quantify the amount of substructure within their distribution using a
two-point correlation function statistic in each of three spaces: configuration
space, line-of-sight velocity space, and four-dimensional phase-space. These
results were compared to those for three sets of subhaloes in the Via Lactea II
Cold Dark Matter simulation defined to represent the luminous dwarfs. We found
no evidence at a significance level above 2-sigma of substructure within the
distribution of the Milky Way satellite galaxies in any of the three spaces.
The "luminous" subhalo sets are more strongly clustered than are the Milky Way
satellites in all three spaces and over a broader range of scales in
four-dimensional phase-space. Each of the "luminous" subhalo sets are clustered
as a result of substructure within their line-of-sight velocity space
distributions at greater than 3-sigma significance, whereas the Milky Way
satellite galaxies are randomly distributed in line-of-sight velocity space.
While our comparison is with only one Cold Dark Matter simulation, the
inconsistencies between the Milky Way satellite galaxies and the Via Lactea II
subhalo sets for all clustering methods suggest a potential new 'small-scale'
tension between Cold Dark Matter theory and the observed Milky Way satellites.
Future work will obtain a more robust comparison between the observed Milky Way
satellites and Cold Dark Matter theory by studying additional simulations.
