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A 2 per cent distance to z = 0.35 by reconstructing baryon acoustic oscillations - II. Fitting techniques

Citation:

Xu X, Padmanabhan N, Eisenstein DJ, Mehta KT, Cuesta AJ. A 2 per cent distance to z = 0.35 by reconstructing baryon acoustic oscillations - II. Fitting techniques. Monthly Notices of the Royal Astronomical Society. 2012;427 :2146-2167.

Date Published:

December 1, 2012

Abstract:

We present results from fitting the baryon acoustic oscillation (BAO)signal in the correlation function obtained from the first applicationof density-field reconstruction to a galaxy redshift survey, namely theSloan Digital Sky Survey (SDSS) Data Release 7 (DR7) luminous red galaxy(LRG) catalogue. Reconstruction works to partially remove the effects ofnon-linear structure growth on the BAO by reconstructing the linearmatter density field from the observed galaxy density field using thecontinuity equation. We also introduce more careful approaches forderiving a suitable covariance matrix and fitting model for galaxycorrelation functions. Our covariance matrix technique guarantees smoothdiagonal and off-diagonal terms by fitting a modified Gaussiancovariance matrix to that calculated from mock catalogues. Our proposedfitting model is effective at removing broad-band effects such asredshift-space distortions, scale-dependent bias and any artefactsintroduced by assuming the wrong model cosmology. These all aid inobtaining a more accurate measurement of the acoustic scale and itserror. We validate these techniques on 160 mock catalogues derived fromthe LasDamas simulations in real and redshift space. We then apply thesetechniques to the DR7 LRG sample and find that the error on the acousticscale decreases from ˜3.5 per cent before reconstruction to˜1.9 per cent after reconstruction. We also see an increase in ourBAO detection confidence from ˜3σ to ˜4σ afterreconstruction with our confidence level in measuring the correctacoustic scale increasing from ˜3σ to ˜5σ. Usingthe mean of the acoustic scale probability distributions produced fromour fits, we find Dv/rs = 8.89 ± 0.31before reconstruction and 8.88 ± 0.17 after reconstruction.

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