A 2 per cent distance toz= 0.35 by reconstructing baryon acoustic oscillations – II. Fitting techniques

Abstract

We present results from fitting the baryon acoustic oscillation (BAO) signal in the correlation function obtained from the first application of density-field reconstruction to a galaxy redshift survey, namely the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) luminous red galaxy (LRG) catalogue. Reconstruction works to partially remove the effects of non-linear structure growth on the BAO by reconstructing the linear matter density field from the observed galaxy density field using the continuity equation. We also introduce more careful approaches for deriving a suitable covariance matrix and fitting model for galaxy correlation functions. Our covariance matrix technique guarantees smooth diagonal and off-diagonal terms by fitting a modified Gaussian covariance matrix to that calculated from mock catalogues. Our proposed fitting model is effective at removing broad-band effects such as redshift-space distortions, scale-dependent bias and any artefacts introduced by assuming the wrong model cosmology. These all aid in obtaining a more accurate measurement of the acoustic scale and its error. We validate these techniques on 160 mock catalogues derived from the LasDamas simulations in real and redshift space. We then apply these techniques to the DR7 LRG sample and find that the error on the acoustic scale decreases from ∼3.5 per cent before reconstruction to ∼1.9 per cent after reconstruction. We also see an increase in our BAO detection confidence from ∼3σ to ∼4σ after reconstruction with our confidence level in measuring the correct acoustic scale increasing from ∼3σ to ∼5σ . Using the mean of the acoustic scale probability distributions produced from our fits, we find D v /r s = 8.89 ± 0.31 before reconstruction and 8.88 ± 0.17 after reconstruction.

Observational probes of cosmic acceleration

“…We have multiplied by the r s of the fiducial ΛCDM model to yield a distance; the sound horizon is predicted to 1.1% from WMAP7. In increasing redshift, data points are from the 6dFGS (Beutler et al, 2011), SDSS-II Xu et al, 2012b), BOSS (Anderson et al, 2012), and WiggleZ (Blake et al, 2011d). The WiggleZ paper also quotes correlated results from multiple redshift bins, but we have chosen to plot only a single combined data point for each survey so that the measurement errors are uncorrelated.…”

“…Kazin et al (2010b) analyzed the DR7 LRG sample with the correlation function (as did Martínez et al 2009), achieving consistent results. A recent reanalysis of the DR7 sample by Padmanabhan et al (2012) and Xu et al (2012b) improved the distance precision to 1.9% by applying the reconstruction technique described in §4.3.3 below.…”

Modelling the number density of Hαemitters for future spectroscopic near-IR space missions

“…Indeed, in recent years, the BAO technique has seen a dramatic improvement in capability owing to the increase in volume probed by galaxy surveys (e.g. Cole et al 2005;Glazebrook et al 2005;Eisenstein et al 2005;Percival et al 2007Percival et al , 2010Blake et al 2011a,b;Padmanabhan et al 2012;Xu et al 2012;Kazin et al 2013Kazin et al , 2014Anderson et al 2014).…”

L-PICOLA: A parallel code for fast dark matter simulation

“…In any real application this is further compounded by the effect of RSD. As such, a much more common solution is to use a set of detailed galaxy simulations, otherwise known as mock catalogues (mocks), to either fully estimate the covariance matrix or as the basis for an empirically motivated analytic fit (Xu et al, 2012).…”