Clustering of photometric luminous red galaxies - I. Growth of structure and baryon acoustic feature

The possibility of measuring redshift-space distortions (RSDs) using photometric data has been recently highlighted. This effect complements and significantly alters the detectability of baryon acoustic oscillations (BAO) in photometric surveys. In this paper we present measurements of the angular correlation function of luminous red galaxies (LRGs) in the photometric catalogue of the final data release [data release 7 (DR7)] of the Sloan Digital Sky Survey II (SDSS-II). The sample compromises similar to 1.5 x 106 LRGs distributed in 0.45 < z < 0.65, with a characteristic photometric error of similar to 0.05. Our measured correlation centred at z= 0.55 is in very good agreement with predictions from standard cold dark matter (CDM) in a broad range of angular scales, 05 < 0 < 6 degrees. We find that the growth of structure can indeed be robustly measured, with errors matching expectations. The velocity growth rate is recovered as fs8= 0.53 +/- 0.42 when no prior is imposed on the growth factor and the background geometry follows a CDM model with 7-year Wilkinson Microwave Anisotropy Probe (WMAP7)+SNIa priors. This is compatible with the corresponding General Relativity (GR) prediction fs8= 0.45 for our fiducial cosmology. If we adopt a parametrization such that f=Omega(gamma)(m)(z), with gamma approximate to 0.55 in GR, and combine our fs8 measurement with the corresponding ones from spectroscopic LRGs at lower redshifts, we obtain gamma = 0.54 +/- 0.17. In addition we find evidence for the presence of the baryon acoustic feature matching the amplitude, location and shape of CDM predictions. The photometric BAO feature is detected with 98 per cent confidence level at z= 0.55.