The disk and halo densities at the plane from star-counts in the Galactic poles

Four determinations of the density distribution D(Z) with height from the plane at the solar circle for dwarfs with absolute magnitudes of (MV) ≅ +4 to +5 are combined. The four determinations are in good agreement. The data extend to Z = 10 kpc. The gradient, dlog D(Z)/dZ, changes continuously over the observed range of Z; the gradient flattens with increasing Z. Calculated density distributions for discrete kinematic samples with σ(W) values of 17, 42, and 90 km s-1 provide a unique fit to the data, giving density normalizations at Z = 0 of 1:0.11:0.005. The authors identify the σ(W) = 17 km s-1 component with the old thin disk (scale height ≡270 pc), the σ(W) = 42 km s-1 component with the thick disk (scale height ≡940 pc), and the σ(W) = 90 km s-1 component with the extreme halo (scale height at ≡3.2 kpc). The mass of the stellar component in the halo is estimated to be ≡3×109M_sun;, comprising less than ≡2% of the total galactic mass. From two normalizations the local density of halo stars is between 1×105M_sun; kpc-3 and 2.5×105M_sun; kpc-3, agreeing well with previous values by Schmidt and by Eggen from widely different methods.