Reconstructing Linear Baryon Acoustic Oscillations

The London Relativity and Cosmology Seminar
Angela Burden (Portsmouth)
April 29th, 2015 at 16:30
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Reconstructing an estimate of linear Baryon Acoustic Oscillations (BAO) from an evolved galaxy field has become a standard technique in recent analyses. By partially removing non-linear damping caused by bulk motions, the real-space BAO peak in the correlation function is sharpened, and oscillations in the power spectrum are visible to smaller scales. In turn these lead to stronger measurements of the BAO scale. Future surveys are being designed assuming that this improvement has been applied, and this technique is therefore of critical importance for future BAO measurements. A number of reconstruction techniques are available, but the most widely used is a simple algorithm that decorrelates large-scale and small-scale modes approximately removing the bulk-flow displacements by moving the overdensity field (Eisenstein et al. 2006). I will present an overview of the methods currently used within the BOSS collaboration before presenting a new fast iterative FFT-based reconstruction algorithm that allows for nonparallel redshift-space distortions (RSD). The iterative reconstruction scheme converges in two iterations for the mock samples, corresponding to BOSS CMASS DR11 galaxy survey data, when we start with an approximation of the RSD. This Fast Fourier Transform based method provides a better estimate of the real space displacement field than a configuration space method that uses finite difference routines to compute the potential for the same grid resolution. Finally I show that a lognormal transform of the overdensity, used as a proxy for the linear overdensity, is beneficial in estimating the full displacement field from a dense sample of tracers. However the lognormal transform of the overdensity does not perform well when estimating the displacements from sparser simulations with a more realistic galaxy density. - G. O. Jones 516