The radial number density and flattening of the Milky Way ’ s stellar halo is measured with \mathrm { 5351 } metal-poor ( [ Fe/H ] < -1 ) K giants from LAMOST DR3 , using a nonparametric method which is model independent and largely avoids the influence of halo substucture .
The number density profile is well described by a single power law with index 5.03 ^ { +0.64 } _ { -0.64 } , and flattening that varies with radius .
The stellar halo traced by LAMOST K giants is more flattened at smaller radii , and becomes nearly spherical at larger radii .
The flattening , q , is about 0.64 , 0.8 , 0.96 at r = 15 , 20 and 30 kpc ( where r = \sqrt { R ^ { 2 } + \left [ Z / q \left ( r \right ) \right ] ^ { 2 } } ) , respectively .
Moreover , the leading arm of the Sagittarius dwarf galaxy tidal stream in the north , and the trailing arm in the south , are significant in the residual map of density distribution .
In addition , an unknown overdensity is identified in the residual map at ( R , Z ) = ( 30,15 ) kpc .