Euclid preparation. Decomposing components of the extragalactic background light using multi-band intensity mapping cross-correlations

TL;DR

This work develops a forward multi-component halo-model to decompose near-infrared EBL fluctuations into IHL, IGL, and EoR contributions by jointly analyzing SPHEREx intensity maps with tomographic cosmic shear and galaxy clustering. It leverages cross-spectra across ten SPHEREx bands to break degeneracies, with IHL showing strong correlation to the lensing field, IGL moderately correlated, and EoR largely uncorrelated, enabling robust component separation. Mock SPHEREx-Euclid data analyzed via MCMC recover fiducial parameters within 1σ and tighten IHL and EoR constraints by up to ~35%, extending SFRD constraints to z~11. The approach also provides a pathway to control dominant systematics (DGL, shot noise, shear calibration, intrinsic alignments) through cross-correlation measurements, highlighting significant gains for component-resolved EBL science. Overall, the framework offers a principled method to study intra-halo light, faint galaxy populations, and early star-formation history in the EoR.

Abstract

The extragalactic background light (EBL) fluctuations in the optical/near-IR encode the cumulative integrated galaxy light (IGL), diffuse intra-halo light (IHL), and high-$z$ sources from the epoch of reionisation (EoR), but they are difficult to disentangle with auto-spectra alone. We aim to decompose the EBL into its principal constituents using multi-band intensity mapping combined with cosmic shear and galaxy clustering. We develop a joint halo-model framework in which IHL follows a mass- and redshift-dependent luminosity scaling, IGL is set by an evolving Schechter luminosity function, and EoR emission is modelled with Pop II/III stellar emissivities and a binned star-formation efficiency. Using mock surveys in a flat $Λ$CDM cosmology with ten spectral bands spanning 0.75-5.0$\rm μm$ in the NEP deep fields over about 100$°^2$ with source detections down to AB=20.5 for masking, and six redshift bins to $z=2.5$, we fit auto- and cross-power spectra using a MCMC method. The combined SPHEREx$\times$Euclid analysis recovers all fiducial parameters within 1$σ$ and reduces 1$σ$ uncertainties on IHL parameters by 10-35% relative to SPHEREx EBL-only, while EoR star-formation efficiency parameters improve by 20-35%. Cross-correlations reveal a stronger coupling of IHL than IGL to the shear field, enhancing component separation; conversely, the EoR contribution shows negligible correlation with cosmic shear and galaxy clustering, aiding its isolation in the EBL. Relative to the SPHEREx EBL-only case, the inferred IHL fraction as a function of halo mass is significantly tightened over $10^{11}-10^{14} M_{\odot}$, with uncertainties reduced by 5-30%, and the resulting star-formation rate density constraints extend to $z\sim 11$, with uncertainty reductions of 22-31%.

Figures (11)

• Figure 1: Kernel of different EBL components and cosmic shear signal as functions of redshift. Left: Kernels of IHL (upper) and IGL (lower) signals in EBL (IGL with masking down to AB = 20.5), respectively. Right: Kernels of the galaxy clustering (upper) and cosmic shear (lower), respectively.
• Figure 2: Components of the EBL anisotropy power spectrum at 2.2 $\micron$. Here, $D_{\ell}=\ell\,(\ell+1)\,C_{\ell}/2\pi$. The blue solid line denotes the total power spectrum with noise, the green, red, and purple dashed lines denote the power spectra of the IHL, IGL, and EoR signals, respectively. DGL is shown as a brown dotted line, for an intensity level comparable to that of the NEP deep field. The shot noise and instrument noise are shown with pink and grey dash-dotted lines, respectively. The orange crosses with error bars represent mock SPHEREx data.
• Figure 3: Luminosity functions obtained using the best-fit parameters are taken from Helgason12. The dashed and dotted vertical lines are the magnitude depths of the SPHEREx deep field and all-sky survey, respectively.
• Figure 4: Luminosity mass density $l_\nu$ as a function of the rest-frame wavelength $\lambda$ for Pop II (Left) and Pop III (Right) stars at $z = 10$. The black solid and dashed lines are the total $l_\nu$ from the stellar nebulae and the IGM. The coloured lines are the various components of stellar nebulae emission: the direct emission from the stars, $\rm{Ly}\alpha$ line, and free-free, free-bound and two-photon processes. We set $f_{\rm esc}$ = 0.2 for both Pop II and Pop III cases.
• Figure 5: Components of the cosmic shear power spectrum for the tomographic redshift bin with $0.4\!<\!z_{\rm ph}\!\le\!0.6$. The blue and green solid lines denote the total power spectrum with noise and the power spectrum of the signal, respectively. The additive shot-noise is shown as a pink dotted line. The red dashed, brown dashed, and purple dot-dashed curves are the power spectra of gravitational-gravitational, intrinsic-intrinsic, and gravitational-intrinsic power spectra, respectively. Note that the value of $C_{\rm GI}(\ell)$ is negative. The orange crosses with error bars represent mock cosmic shear data without shot noise.