GALAXY CLUSTERING IN THE COMPLETED SDSS REDSHIFT SURVEY: THE DEPENDENCE ON COLOR AND LUMINOSITY

Abstract

We measure the luminosity and color dependence of galaxy clustering in the largest-ever galaxy redshift survey, the main galaxy sample of the Sloan Digital Sky Survey Seventh Data Release. We focus on the projected correlation function w p ( r p ) of volume-limited samples, extracted from the parent sample of ∼700,000 galaxies over 8000 deg 2 , extending up to redshift of 0.25. We interpret our measurements using halo occupation distribution (HOD) modeling assuming a ΛCDM cosmology (inflationary cold dark matter with a cosmological constant). The amplitude of w p ( r p ) grows slowly with luminosity for L < L * and increases sharply at higher luminosities, with a large-scale bias factor b (> L ) × (σ 8 /0.8) = 1.06 + 0.21( L / L * ) 1.12 , where L is the sample luminosity threshold. At fixed luminosity, redder galaxies exhibit a higher amplitude and steeper correlation function, a steady trend that runs through the "blue cloud" and "green valley" and continues across the "red sequence." The cross-correlation of red and blue galaxies is close to the geometric mean of their autocorrelations, dropping slightly below at r p < 1 h −1 Mpc. The luminosity trends for the red and blue galaxy populations separately are strikingly different. Blue galaxies show a slow but steady increase of clustering strength with luminosity, with nearly constant shape of w p ( r p ). The large-scale clustering of red galaxies shows little luminosity dependence until a sharp increase at L > 4 L * , but the lowest luminosity red galaxies (0.04–0.25 L * ) show very strong clustering on small scales ( r p < 2 h −1 Mpc). Most of the observed trends can be naturally understood within the ΛCDM+HOD framework. The growth of w p ( r p ) for higher luminosity galaxies reflects an overall shift in the mass scale of their host dark matter halos, in particular an increase in the minimum host halo mass M min . The mass at which a halo has, on average, one satellite galaxy brighter than L is M 1 ≈ 17 M min ( L ) over most of the luminosity range, with a smaller ratio above L * . The growth and steepening of w p ( r p ) for redder galaxies reflects the increasing fraction of galaxies that are satellite systems in high-mass halos instead of central systems in low-mass halos, a trend that is especially marked at low luminosities. Our extensive measurements, provided in tabular form, will allow detailed tests of theoretical models of galaxy formation, a firm grounding of semiempirical models of the galaxy population, and new constraints on cosmological parameters from combining real-space galaxy clustering with mass-sensitive statistics such as redshift-space distortions, cluster mass-to-light ratios, and galaxy–galaxy lensing.