In addition to optical photometry of unprecedented quality , the Sloan Digital Sky Survey ( SDSS ) is producing a massive spectroscopic database which already contains over 280,000 stellar spectra .
Using effective temperature and metallicity derived from SDSS spectra for \sim 60,000 F and G type main sequence stars ( 0.2 < g - r < 0.6 ) , we develop polynomial models , reminiscent of traditional methods based on the UBV photometry , for estimating these parameters from the SDSS u - g and g - r colors .
These estimators reproduce SDSS spectroscopic parameters with a root-mean-square scatter of 100 K for effective temperature , and 0.2 dex for metallicity ( limited by photometric errors ) , which are similar to random and systematic uncertainties in spectroscopic determinations .
We apply this method to a photometric catalog of coadded SDSS observations and study the photometric metallicity distribution of \sim 200,000 F and G type stars observed in 300 deg ^ { 2 } of high Galactic latitude sky .
These deeper ( g < 20.5 ) and photometrically precise ( \sim 0.01 mag ) coadded data enable an accurate measurement of the unbiased metallicity distribution for a complete volume-limited sample of stars at distances between 500 pc and 8 kpc .
The metallicity distribution can be exquisitely modeled using two components with a spatially varying number ratio , that correspond to disk and halo .
The best-fit number ratio of the two components is consistent with that implied by the decomposition of stellar counts profiles into exponential disk and power-law halo components by Jurić et al .
( 2008 ) .
The two components also possess the kinematics expected for disk and halo stars .
The metallicity of the halo component can be modeled as a spatially invariant Gaussian distribution with a mean of [ Fe / H ] = -1.46 and a standard deviation of \sim 0.3 dex .
The disk metallicity distribution is non-Gaussian , with a remarkably small scatter ( rms \sim 0.16 dex ) and the median smoothly decreasing with distance from the plane from -0.6 at 500 pc to -0.8 beyond several kpc .
Similarly , we find using proper motion measurements that a non-Gaussian rotational velocity distribution of disk stars shifts by \sim 50 km/s as the distance from the plane increases from 500 pc to several kpc .
Despite this similarity , the metallicity and rotational velocity distributions of disk stars are not correlated ( Kendall ’ s \tau = 0.017 \pm 0.018 ) .
This absence of a correlation between metallicity and kinematics for disk stars is in a conflict with the traditional decomposition in terms of thin and thick disks , which predicts a strong correlation ( \tau = -0.30 \pm 0.04 ) at \sim 1 kpc from the mid-plane .
Instead , the variation of the metallicity and rotational velocity distributions can be modeled using non-Gaussian functions that retain their shapes and only shift as the distance from the mid-plane increases .
We also study the metallicity distribution using a shallower ( g < 19.5 ) but much larger sample of close to three million stars in 8500 sq .
deg .
of sky included in SDSS Data Release 6 .
The large sky coverage enables the detection of coherent substructures in the kinematics–metallicity space , such as the Monoceros stream , which rotates faster than the LSR , and has a median metallicity of [ Fe / H ] = -0.95 , with an rms scatter of only \sim 0.15 dex .
We extrapolate our results to the performance expected from the Large Synoptic Survey Telescope ( LSST ) and estimate that the LSST will obtain metallicity measurements accurate to 0.2 dex or better , with proper motion measurements accurate to \sim 0.2-0.5 mas/yr , for about 200 million F/G dwarf stars within a distance limit of \sim 100 kpc ( g < 23.5 ) .