The Century Survey Galactic Halo Project. III. A Complete 4300 Deg(2) Survey Of Blue Horizontal Branch Stars In The Metal-Weak Thick Disk And Inner Halo

Abstract

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.