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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 ∼1.5 × 106 LRGs distributed in 0.45 < z < 0.65, with a characteristic photometric error of ∼0.05. Our measured correlation centred at z= 0.55 is in very good agreement with predictions from standard Λcold dark matter (ΛCDM) in a broad range of angular scales, 0bsl000645 < θ < 6°. We find that the growth of structure can indeed be robustly measured, with errors matching expectations. The velocity growth rate is recovered as fσ8= 0.53 ± 0.42 when no prior is imposed on the growth factor and the background geometry follows a ΛCDM model with 7-year Wilkinson Microwave Anisotropy Probe (WMAP7)+SNIa priors. This is compatible with the corresponding General Relativity (GR) prediction fσ8= 0.45 for our fiducial cosmology. If we adopt a parametrization such that fγm(z), with γ≈ 0.55 in GR, and combine our fσ8 measurement with the corresponding ones from spectroscopic LRGs at lower redshifts, we obtain γ= 0.54 ± 0.17. In addition we find evidence for the presence of the baryon acoustic feature matching the amplitude, location and shape of ΛCDM predictions. The photometric BAO feature is detected with 98 per cent confidence level at z= 0.55.