As part of a global analysis of deep star counts to constrain scenarii of galaxy formation and evolution , we investigate possible links between the galactic spheroid and the dark matter halo .
A wide set of deep star counts at high and intermediate galactic latitudes is used to determine the large scale density law of the spheroid .
Assuming a power density law , the exponent , flattening , local density and IMF slope of this population are estimated .
The estimation is checked for robustness against contamination of star counts by the thick disc population .
Contamination effects are derived from a model of population synthesis under a broad variety of thick disc parameters .
The parameter fit is based on a maximum likelihood criterion .
The best fit spheroid density law has a flattening of 0.76 , a power index of 2.44 .
There is a significant degeneracy between these two parameters .
The data are also compatible with a slightly less flattened spheroid ( c/a = 0.85 ) , in combination with a larger power index ( 2.75 ) .
A flatter spheroid ( c/a = 0.6 ) with a power index of 2 is not excluded either .
We also constrain the spheroid IMF slope \alpha to be 1.9 \pm 0.2 , leading to a local density of 1.64 10 ^ { -4 } stars pc ^ { -3 } and a mass density of 4.15 10 ^ { -5 } M _ { \odot } pc ^ { -3 } .
With this slope the expected mass density of brown dwarfs in the halo makes a negligible part of the dark matter halo , as already estimated from microlensing surveys .

So , as star count data progresses in depth and extent , the picture of the spheroid star population that comes out points to a shape quite compatible with what we know about the distribution of baryonic dark matter if it is made of stellar remnants , suggesting a common dynamical origin .