Cosmic Near-infrared Background Tomography with SPHEREx Using Galaxy Cross-correlations

TL;DR

This paper forecasts the ability of SPHEREx to perform redshift tomography of the near-infrared extragalactic background light through galaxy cross-correlations, enabling insights into cosmic star formation history up to redshift 6.

Contribution

It introduces a method to use galaxy cross-correlations with SPHEREx data for EBL spectral and redshift tomography, providing forecasts for detection sensitivity and potential scientific insights.

Findings

EBL spectrum detectable up to z~6

High-significance cross-power spectrum measurement up to z~10

Constraints on stellar evolution and galaxy spectra across redshifts

Abstract

The extragalactic background light (EBL) consists of integrated light from all sources of emission throughout the history of the universe. At near-infrared wavelengths, the EBL is dominated by stellar emission across cosmic time; however, the spectral and redshift information of the emitting sources is entangled and cannot be directly measured by absolute photometry or fluctuation measurements. Cross-correlating near-infrared maps with tracers of known redshift enables EBL redshift tomography, as EBL emission will only correlate with external tracers from the same redshift. Here, we forecast the sensitivity of probing the EBL spectral energy distribution as a function of redshift by cross-correlating the upcoming near-infrared spectro-imaging survey, SPHEREx, with several current and future galaxy redshift surveys. Using a model galaxy luminosity function, we estimate the cross power spectrum clustering amplitude on large scales, and forecast that the near-infrared EBL spectrum can be detected tomographically out to $z\sim 6$. We also predict a high-significance measurement ($\sim 10^2$-$10^4\sigma$) of the small-scale cross-power spectrum out to $z\sim 10$. The amplitudes of the large-scale cross power spectra can constrain the cosmic evolution of the stellar synthesis process through both continuum and the line emission, while on the nonlinear and Poisson noise scales, the high-sensitivity measurements can probe the mean spectra associated with the tracer population across redshift.