The Century Survey Galactic Halo Project Iii: a Complete 4300 Deg Survey 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 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 dvrot/d|Z| = −28± 3.4 km s −1 in the region |Z| < 6 kpc, and a density scale height of hZ = 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. We infer the density of halo and thick disk BHB stars is 104± 37 kpc near the Sun, and the relative normalization of halo to thick-disk BHB stars is 4± 1% near the Sun. Subject headings: stars: early types — stars: horizontal-branch — Galaxy: stellar content — Galaxy: halo