The Century Survey Galactic Halo Project. Iii. A Complete 4300 Deg²survey of Blue Horizontal Branch Stars in the Metal-Weak Thick Disk and Inner Halo

We present a complete spectroscopic survey of 2414 2MASS-selected blue horizontal branch (BHB) candidates selected over 4300 deg 2 of the sky. We identify 655 BHB stars in this non-kinematically selected sample. We calculate the luminosity function of field BHB stars, and find evidence for very few hot BHB stars in the field. The BHB stars located at a distance from the Galactic plane | Z | < 4 kpc trace what is clearly a metal-weak thick disk population, with a mean metallicity of [Fe/H] = −1.7, a rotation velocity gradient of dv rot / d | Z | = −28 ± 3.4 km s −1 in the region | Z | < 6 kpc, and a density scale height of h Z = 1.26 ± 0.1 kpc. The BHB stars located at 5 < | Z | < 9 kpc are a predominantly inner-halo population, with a mean metallicity of [Fe/H] = −2.0 and a mean Galactic rotation of −4 ± 31 km s −1 . We infer the density of halo and thick disk BHB stars is 104 ± 37 kpc −3 near the Sun, and the relative normalization of halo to thick-disk BHB stars is 4 ± 1% near the Sun.