Cosmology with the SPHEREX All-Sky Spectral Survey

TL;DR

The paper outlines SPHEREx, a small-satellite all-sky near-infrared spectroscopic survey using LVFs to obtain low- and mid-resolution spectra across 0.75–4.8 μm, with a two-year mission delivering four full-sky spectral maps. It presents a comprehensive simulation and data-processing pipeline to build a 3D galaxy catalog from cross-matched external catalogs, forecast cosmological constraints (notably on f_NL_loc, n_s, and Omega_K) via power spectrum and bispectrum analyses, and assess systematic effects. It also details the SPHEREx Galactic Ice Investigation and the Extragalactic Background Light/Line-Intensity Mapping science programs, plus synergies with Euclid and WFIRST and the mission’s enduring legacy in a broad spectral data-base. The results demonstrate competitive inflationary constraints, robust handling of systematics, and transformative capabilities for ice science and EBL studies, establishing SPHEREx as a foundational archival resource for the community.

Abstract

SPHEREx (Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer) ( http://spherex.caltech.edu ) is a proposed all-sky spectroscopic survey satellite designed to address all three science goals in NASA's Astrophysics Division: probe the origin and destiny of our Universe; explore whether planets around other stars could harbor life; and explore the origin and evolution of galaxies. SPHEREx will scan a series of Linear Variable Filters systematically across the entire sky. The SPHEREx data set will contain R=40 spectra fir 0.75$<λ<$4.1$μ$m and R=150 spectra for 4.1$<λ<$4.8$μ$m for every 6.2 arc second pixel over the entire-sky. In this paper, we detail the extra-galactic and cosmological studies SPHEREx will enable and present detailed systematic effect evaluations. We also outline the Ice and Galaxy Evolution Investigations.

Figures (23)

• Figure 1: SPHEREx completes an All-Sky map in a step and repeat fashion, one targeted observation at a time, separated by spacecraft slew maneuvers.
• Figure 2: SPHEREx scientifically required point source sensitivity has large margin over the estimated instrument performance. We show above the instrument requirement (red dashed line) and the MEV (solid colored curve) and CBE (dashed current curve) performance. The Maximum Expected Value (MEV) performance refers to the instrument performance based on specifications that each sub-system can meet with contingency. The Current Best Estimated (CBE) performance is the instrument performance based on currently estimated sub-system performance. The scientific margin is defined as the difference between MEV Performance and the Instrument Requirement. The Band 4 sensitivity easily meets the 12 AB mag (5σ) requirement, and will return hundreds of thousands of high-quality ice absorption spectra (see Sec. \ref{['sec:ice_investigation']}).
• Figure 3: By precisely measuring the spatial clustering of galaxies, SPHEREx will measure primordial non-Gaussianity described conveniently by the parameter $f_{\rm NL}^{\rm loc}$ . This plot shows two simulated distributions of matter (color scales) and galaxies (blue dots) for different values of $f_{\rm NL}^{\rm loc}$ . By precisely measuring the clustering of galaxies over a volume more than $10^5$ times larger than depicted here, SPHEREx will measure $f_{\rm NL}^{\rm loc}$ to high accuracy.
• Figure 4: SPHEREx determines the redshifts of WISE (diamonds) and Pan-STARSS/DES (circles) galaxies by fitting their measured spectra. Each redshift is assigned an error, a process we have extensively simulated from the COSMOS galaxy catalog. The determination is strongly driven by the 1.6 $\mu$m bump, so the target redshift range is well-matched to the 0.75$\leq\lambda\leq$4.1 $\mu$m wavelength coverage. We require a minimum redshift error $\Delta z/(1+z)$ = 0.5% to access the finest useful physical scales, which requires a spectral resolution of 35.
• Figure 5: Overview of the planned SPHEREx analysis pipeline, going from raw telemetered data to calibrated multi-wavelenth images and various science studies.