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 \pm 0.010 ( –0.125 \pm 0.008 ) dex kpc ^ { -1 } 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 ^ { -1 } 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 .