The flat-sky approximation to galaxy number counts -- redshift space correlation function

Abstract

We study the flat-sky approximation for galaxy number counts including relativistic effects, and assess its performance and accuracy with respect to the full-sky result. We find an agreement of up to 5% for the local and lensing contributions to the 2-point correlation function and its multipoles at $z>0.5$, and up to 1% for the multipoles alone at $z>1$ and separations $\lesssim 250$ Mpc/$h$, with a speed-up of over a factor of 1000. Using a semi-analytic method, which has been implemented in a new version of the code COFFE, along with the Limber approximation for the integrated contributions, we further increase the performance, allowing the computation of the flat-sky multipoles to be done over 10000 times faster than in the full-sky calculation, which could be used to greatly speed-up Markov chain Monte Carlo sampling for cosmological parameter estimation.

32 pages, 8 figures. Fixed missing factor of 2 in density-lensing eq. (2.15). Code available at https://github.com/JCGoran/coffe

References in corpus (6)

• The DESI Experiment Part I: Science,Targeting, and Survey Design
• Extended Limber Approximation
• New Perspective on Galaxy Clustering as a Cosmological Probe: General Relativistic Effects
• Searching for modified growth patterns with tomographic surveys
• 2-FAST: Fast and accurate computation of projected two-point functions
• The Flat Sky Approximation to Galaxy Number Counts

Cited by in corpus (5)

• The observed galaxy power spectrum in General Relativity
• Large Scale Limit of the Observed Galaxy Power Spectrum
• Small scale effects in the observable power spectrum at large angular scales
• Relativistic imprints on dispersion measure space distortions
• Impact of lensing magnification on the analysis of galaxy clustering in redshift space