The Angular Correlation Function of Galaxies from Early Sloan Digital Sky Survey Data

The Sloan Digital Sky Survey is one of the first multicolor photometric and spectroscopic surveys designed to measure the statistical properties of galaxies within the local universe. In this paper we present some of the initial results on the angular two-point correlation function measured from the early SDSS galaxy data. The form of the correlation function, over the magnitude interval 18 < r* < 22, is shown to be consistent with results from existing wide-field, photographic-based surveys and narrower CCD galaxy surveys. On scales between 1' and 1° the correlation function is well described by a power law with an exponent of ≈-0.7. The amplitude of the correlation function, within this angular interval, decreases with fainter magnitudes in good agreement with analysis from existing galaxy surveys. There is a characteristic break in the correlation function on scales of approximately 1°-2°. On small scales, θ < 1′, the SDSS correlation function does not appear to be consistent with the power-law form fitted to the 1′ < θ < 0.°5 data. With a data set that is less than 2% of the full SDSS survey area, we have obtained high-precision measurements of the power-law angular correlation function on angular scales 1′ < θ < 1°, which are robust to systematic uncertainties. Because of the limited area and the highly correlated nature of the error covariance matrix, these initial results do not yet provide a definitive characterization of departures from the power-law form at smaller and larger angles. In the near future, however, the area of the SDSS imaging survey will be sufficient to allow detailed analysis of the small- and large-scale regimes, measurements of higher order correlations, and studies of angular clustering as a function of redshift and galaxy type.