3-dimensional spherical analyses of cosmological spectroscopic surveys

TL;DR

This paper compares spherical harmonic tomography and spherical Fourier Bessel methods for analyzing deep, wide spectroscopic surveys, assessing their effectiveness and implementation sensitivities for cosmological parameter constraints.

Contribution

It provides a detailed comparison of SHT and SFB methods, including their sensitivities, approximations, and suitability for future cosmological surveys.

Findings

Overlapping redshift bins can improve SHT constraints with few bins.

SFB constraints are robust to the distance-redshift relation.

SHT is more sensitive near survey boundaries; SFB captures beyond-smooth spectrum information.

Abstract

Spectroscopic redshift surveys offer great prospects for constraining the dark sector in cosmology. Future surveys will however be both deep and wide and will thus require an analysis in 3-dimensional spherical geometry. We review and compare several methods which have been proposed in the literature for this purpose, focusing in particular on implementations of the spherical harmonic tomography (SHT) power spectrum $C^{i j}_{l}$ and the spherical Fourier Bessel (SFB) power spectrum $C_{l} (k, k')$. Using a Fisher analysis, we compare the forecasted constraints on cosmological parameters using these statistics. These constraints typically rely on approximations such as the Limber approximation and make specific choices in the numerical implementation of each statistic. Using a series of toy models, we explore the applicability of these approximations and study the sensitivity of the SHT and SFB statistics to the details of their implementation. In particular, we show that overlapping redshift bins may improve cosmological constraints using the SHT statistic when the number of bins is small, and that the SFB constraints are quite robust to changes in the assumed distance-redshift relation. We also find that the SHT can be tailored to be more sensitive to modes at redshifts close to the survey boundary, while the SFB appears better suited to capture information beyond the smooth shape of the power spectrum. In this context, we discuss the pros and cons of the different techniques and their impact on the design and analysis of future wide field spectroscopic surveys.