Metallicity Gradients of Thick Disk Dwarf Stars
  We examine the metallicity distribution of the Galactic thick disk using F,
G, and K dwarf stars selected from the Sloan Digital Sky Survey, Data Release
8. Using the large sample of dwarf stars with proper motions and
spectroscopically determined stellar parameters, metallicity gradients in the
radial direction for various heights above the Galactic plane and in the
vertical direction for various radial distances from the Galaxy center have
been found. In particular, we find a vertical metallicity gradient of -0.113
+/- 0.010 (-0.125 +/- 0.008) dex/kpc using an isochrone (photometric) distance
determination in the range 1 < |Z| < 3 kpc, which is the vertical height range
most consistent with the thick disk of our Galaxy. In the radial direction, we
find metallicity gradients between +0.02 and +0.03 dex/kpc for bins in the
vertical direction between 1 < |Z| < 3 kpc. Both of these results agree with
similar values determined from other populations of stars, but this is the
first time a radial metallicity gradient for the thick disk has been found at
these vertical heights. We are also able to separate thin and thick disk stars
based on kinematic and spatial probabilities in the vertical height range where
there is significant overlap of these two populations. This should aid further
studies of the metallicity gradients of the disk for vertical heights lower
than those studied here but above the solar neighborhood. Metallicity gradients
in the thin and thick disks are important probes into possible formation
scenarios for our Galaxy and a consistent picture is beginning to emerge from
results using large spectroscopic surveys, such as the ones presented here.
