The Milky Way stellar halo out to 40 kpc : Squashed, broken but smooth
  We introduce a new maximum likelihood method to model the density profile of
Blue Horizontal Branch and Blue Straggler stars and apply it to the Sloan
Digital Sky Survey Data Release 8 (DR8) photometric catalogue. There are a
large number (20,000) of these tracers available over an impressive 14,000
square degrees in both Northern and Southern Galactic hemispheres, and they
provide a robust measurement of the shape of the Milky Way stellar halo. After
masking out stars in the vicinity of the Virgo Overdensity and the Sagittarius
stream, the data are consistent with a smooth, oblate stellar halo with a
density that follows a broken power-law. The best fitting model has an inner
slope = 2.3 and an outer slope = 4.6, together with a break radius occurring at
27 kpc and a constant halo flattening (that is, ratio of minor axis to major
axis) of q = 0.6. Although a broken power-law describes the density fall-off
most adequately, it is also well fit by an Einasto profile. There is no strong
evidence for variations in flattening with radius, or for triaxiality of the
stellar halo.
