Date Published:

July 1, 2012

Abstract:

We analyse the density field of galaxies observed by the Sloan DigitalSky Survey (SDSS)-III Baryon Oscillation Spectroscopic Survey (BOSS)included in the SDSS Data Release Nine (DR9). DR9 includes spectroscopicredshifts for over 400 000 galaxies spread over a footprint of 3275deg². We identify, characterize and mitigate the impact ofsources of systematic uncertainty on large-scale clusteringmeasurements, both for angular moments of the redshift-space correlationfunction, ξ_ℓ(s), and the spherically averaged powerspectrum, P(k), in order to ensure that robust cosmological constraintswill be obtained from these data. A correlation between the projecteddensity of stars and the higher redshift (0.43 < z < 0.7) galaxysample (the approximately constant stellar mass threshold 'CMASS'sample) due to imaging systematics imparts a systematic error that islarger than the statistical error of the clustering measurements atscales s > 120 h^-1 Mpc or k < 0.01 h Mpc^-1.We find that these errors can be ameliorated by weighting galaxies basedon their surface brightness and the local stellar density. Theclustering of CMASS galaxies found in the Northern and Southern Galacticfootprints of the survey generally agrees to within 2σ. We usemock galaxy catalogues that simulate the CMASS selection function todetermine that randomly selecting galaxy redshifts in order to simulatethe radial selection function of a random sample imparts the leastsystematic error on ξ_ℓ(s) measurements and that thissystematic error is negligible for the spherically averaged correlationfunction, ξ₀. We find a peak in ξ₀ ats˜ 200 h^-1 Mpc, with a corresponding feature withperiod ˜0.03 h Mpc^-1 in P(k), and find features atleast as strong in 4.8 per cent of the mock galaxy catalogues,concluding this feature is likely to be a consequence of cosmicvariance. The methods we recommend for the calculation of clusteringmeasurements using the CMASS sample are adopted in companion papers thatlocate the position of the baryon acoustic oscillation feature,constrain cosmological models using the full shape of ξ₀and measure the rate of structure growth.

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