A measurement of the intrahalo light fraction with near-infrared background anisotropies

TL;DR

This study measures near-infrared background anisotropies across large scales, finding they can be explained by intrahalo stars rather than new galaxy populations, thus shedding light on the distribution of diffuse light in dark matter halos.

Contribution

It provides the first measurement of anisotropy power spectrum on large scales and attributes the observed fluctuations to intrahalo stars, not faint galaxies or new sources.

Findings

Clustering amplitude exceeds model predictions from known sources.

Shot-noise level matches expectations from faint galaxies.

Intrahalo light fraction is estimated at 0.07 to 0.2% in dark matter halos.

Abstract

Unresolved near-infrared background anisotropies are expected to have contributions from the earliest galaxies during reionization and faint, dwarf galaxies at intermediate redshifts. Previous measurements were unable to conclusively pinpoint the dominant origin because they did not sample spatial scales that were sufficiently large to distinguish between these two possibilities. Here we report a measurement of the anisotropy power spectrum from sub-arcminute to one degree angular scales and find the clustering amplitude to be larger than the model predictions involving the two existing explanations. As the shot-noise level of the power spectrum is consistent with that expected from faint galaxies, a new source population on the sky is not necessary to explain the observations. A physical mechanism that increases the clustering amplitude, however, is needed. Motivated by recent results related to the extended stellar light profile in dark matter halos, we consider the possibility that the fluctuations originate from diffuse intrahalo stars of all galaxies. We find that the measured power spectrum can be explained by an intrahalo light fraction of 0.07 to 0.2 % relative to the total luminosity in dark matter halos of masses log(M/M_Sun) ~ 9 to 12 at redshifts of ~ 1 to 4.