Angular correlation function of 1.5 million luminous red galaxies: clustering evolution and a search for baryon acoustic oscillations

We present the angular correlation function measured from photometric samples comprising 1562 800 luminous red galaxies (LRGs). Three LRG samples were extracted from the Sloan Digital Sky Survey (SDSS) imaging data, based on colour-cut selections at redshifts, z approximate to 0.35, 0.55 and 0.7 as calibrated by the spectroscopic surveys, SDSS-LRG, 2dF-SDSS LRG and QSO (quasi-stellar object) (2SLAQ) and the AA Omega-LRG survey. The galaxy samples cover approximate to 7600 deg(2) of sky, probing a total cosmic volume of approximate to 5.5 h(-3) Gpc(3). The small- and intermediate-scale correlation functions generally show significant deviations from a single power-law fit with a well-detected break at approximate to 1 h(-1) Mpc, consistent with the transition scale between the one-and two-halo terms in halo occupation models. For galaxy separations 1-20 h(-1) Mpc and at fixed luminosity, we see virtually no evolution of the clustering with redshift and the data are consistent with a simple high peaks biasing model where the comoving LRG space density is constant with z. At fixed z, the LRG clustering amplitude increases with luminosity in accordance with the simple high peaks model, with a typical LRG dark matter halo mass 10(13)-10(14) h(-1) M-circle dot. For r < 1 h(-1) Mpc, the evolution is slightly faster and the clustering decreases towards high redshift consistent with a virialized clustering model. However, assuming the halo occupation distribution (HOD) and Lambda cold dark matter (Lambda CDM) halo merger frameworks, similar to 2-3 per cent/Gyr of the LRGs are required to merge in order to explain the small scales clustering evolution, consistent with previous results. At large scales, our result shows good agreement with the SDSS-LRG result of Eisenstein et al. but we find an apparent excess clustering signal beyond the baryon acoustic oscillations (BAO) scale. Angular power spectrum analyses of similar LRG samples also detect a similar apparent large-scale clustering excess but more data are required to check for this feature in independent galaxy data sets. Certainly, if the Lambda CDM model were correct then we would have to conclude that this excess was caused by systematics at the level of Delta w approximate to 0.001-0.0015 in the photometric AA Omega-LRG sample.