The small-scale clustering of luminous red galaxies via cross-correlation techniques

We present the small-scale (0.2-7 h(-1) Mpc) cross-correlations between 32,000 luminous early-type galaxies and a reference sample of 16 million normal galaxies from the Sloan Digital Sky Survey (SDSS). Our method allows us to construct the spherically averaged, real-space cross-correlation function between the spectroscopic luminous red galaxy (LRG) sample and galaxies from the SDSS imaging. We report the cross-correlation as a function of scale, luminosity, and redshift. We find very strong luminosity dependences in the clustering amplitudes, up to a factor of 4 over a factor of 4 in luminosity, and we measure this dependence with a high signal-to-noise ratio. The luminosity dependence of bias is found to depend on scale, with more variation on smaller scales. The clustering as a function of scale is not a power law but instead has a dip at 1 h(-1) Mpc and an excess on small scales. The fraction of red galaxies within the L* sample surrounding LRGs is a strong function of scale, as expected. However, the fraction of red galaxies evolves in redshift similarly on small and large scales, suggesting that cluster and field populations are changing in the same manner. The results highlight the advantage on small scales of using cross-correlation methods as a means of avoiding shot noise in samples of rare galaxies.