The extended Baryon Oscillation Spectroscopic Survey (eBOSS): a cosmological forecast

TL;DR

This paper forecasts the scientific capabilities of the eBOSS survey in measuring cosmological parameters like BAO, RSD, non-Gaussianity, and neutrino mass, highlighting its potential precision and improvements over previous surveys.

Contribution

It provides the first detailed forecast of eBOSS's expected accuracy in key cosmological measurements using multiple tracers and Ly-$a$ forest data.

Findings

eBOSS can achieve 1-2.2% precision in BAO distance measurements.

The survey can constrain $f\sigma_8$ to within 2.5-3.3%.

eBOSS alone can measure primordial non-Gaussianity with $\sigma(f_{NL})\sim10-15$.

Abstract

We present a science forecast for the eBOSS survey, part of the SDSS-IV project, which is a spectroscopic survey using multiple tracers of large-scale structure, including luminous red galaxies (LRGs), emission line galaxies (ELGs) and quasars (both as a direct probe of structure and through the Ly-$\alpha$ forest). Focusing on discrete tracers, we forecast the expected accuracy of the baryonic acoustic oscillation (BAO), the redshift-space distortion (RSD) measurements, the $f_{\rm NL}$ parameter quantifying the primordial non-Gaussianity, the dark energy and modified gravity parameters. We also use the line-of-sight clustering in the Ly-$\alpha$ forest to constrain the total neutrino mass. We find that eBOSS LRGs ($0.6<z<1.0$) (combined with the BOSS LRGs at $z>0.6$), ELGs ($0.6<z<1.2$) and Clustering Quasars (CQs) ($0.6<z<2.2$) can achieve a precision of 1%, 2.2% and 1.6% precisions, respectively, for spherically averaged BAO distance measurements. Using the same samples, the constraint on $f\sigma_8$ is expected to be 2.5%, 3.3% and 2.8% respectively. For primordial non-Gaussianity, eBOSS alone can reach an accuracy of $\sigma(f_{\rm NL})\sim10-15$, depending on the external measurement of the galaxy bias and our ability to model large-scale systematic errors. eBOSS can at most improve the dark energy Figure of Merit (FoM) by a factor of $3$ for the Chevallier-Polarski-Linder (CPL) parametrisation, and can well constrain three eigenmodes for the general equation-of-state parameter (Abridged).