Reconstructing the Near-IR Background Fluctuations from known Galaxy Populations using Multiband Measurements of Luminosity Functions

TL;DR

This study models near-infrared background fluctuations from known galaxy populations using multi-band luminosity functions, finding they cannot fully explain observed large-scale clustering, implying a significant contribution from unknown faint sources.

Contribution

It provides a comprehensive empirical model of galaxy luminosity functions across multiple bands and redshifts, and compares predicted fluctuations to observations, highlighting the need for additional sources.

Findings

Known galaxy populations cannot account for large-scale CIB fluctuations.

Fluctuations increase with fainter source removal, indicating higher redshift contributions.

A very faint, highly clustered population likely dominates the unresolved CIB signal.

Abstract

We model fluctuations in the Cosmic Infrared Background (CIB) arising from known galaxy populations using 233 measured UV, optical and NIR luminosity functions (LF) from a variety of surveys spanning a wide range of redshifts. We compare best-fit Schechter parameters across the literature and find clear indication of evolution with redshift. Providing fitting formulae for the multi-band evolution of the LFs out to z~5, we calculate the total emission redshifted into the near-IR bands in the observer frame and recover the observed optical and near-IR galaxy counts to a good accuracy. Our empirical approach, in conjunction with a halo model describing the clustering of galaxies, allows us to compute the fluctuations of the unresolved CIB and compare the models to current measurements. We find that fluctuations from known galaxy populations are unable to account for the large scale CIB clustering signal seen by Spitzer/IRAC and AKARI/IRC and continue to diverge out to larger angular scales. This holds true even if the LFs are extrapolated out to faint magnitudes with a steep faint-end slope all the way to z=8. We also show that removing resolved sources to progressively fainter magnitude limits, isolates CIB fluctuations to increasingly higher redshifts. Our empirical approach suggests that known galaxy populations are not responsible for the bulk of the fluctuation signal seen in the measurements and favors a very faint population of highly clustered sources.