Can the Near-IR Fluctuations Arise from Known Galaxy Populations?

TL;DR

This study investigates whether known galaxy populations can explain the observed near-infrared background fluctuations, concluding they cannot and implying the existence of an unknown, highly clustered faint source population.

Contribution

It provides an empirical analysis showing known galaxy populations are insufficient to explain the large-scale CIB fluctuations, suggesting an unknown source population.

Findings

Known galaxy populations cannot account for the observed fluctuations.

The fluctuation signal likely originates from an unknown, highly clustered faint source population.

The model accurately reproduces galaxy counts but not the clustering signal.

Abstract

Spatial Fluctuations in the Cosmic Infrared Background have now been measured out to sub-degree scales showing a strong clustering signal from unresolved sources. We attempt to explain these measurement by considering faint galaxy populations at z<6 as the underlying sources for this signal using 233 measured UV, optical and NIR luminosity functions (LF) from a variety of surveys covering a wide range of redshifts. We populate the lightcone and 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. Using a halo model for the clustering of galaxies with an underlying LCDM density field, we find that fluctuations from known galaxy populations are unable to account for the large scale CIB clustering signal seen by HST/NICMOS, Spitzer/IRAC and AKARI/IRC and continue to diverge out to larger angular scales. Our purely empirical reconstruction shows that known galaxy populations are not responsible for the bulk of the fluctuation signal seen in the measurements and suggests an unknown population of very faint and highly clustered sources dominating the signal.