Cosmic Infrared Background Fluctuations and Zodiacal Light

TL;DR

This study tests the impact of zodiacal light on near-IR background fluctuations and finds that large-scale power is not caused by zodiacal light, despite some correlation at small scales.

Contribution

It provides a direct observational test of zodiacal light's effect on IR background fluctuations, addressing previous indirect estimates and uncertainties.

Findings

White noise correlates with zodiacal light intensity.

Large-scale power shows no correlation with zodiacal light.

Zodiacal light does not cause large-scale IR background fluctuations.

Abstract

We have performed a specific observational test to measure the effect that the zodiacal light can have on measurements of the spatial fluctuations of the near-IR background. Previous estimates of possible fluctuations caused by zodiacal light have often been extrapolated from observations of the thermal emission at longer wavelengths and low angular resolution, or from IRAC observations of high latitude fields where zodiacal light is faint and not strongly varying with time. The new observations analyzed here target the COSMOS field, at low ecliptic latitude where the zodiacal light intensity varies by factors of $\sim2$ over the range of solar elongations at which the field can be observed. We find that the white noise component of the spatial power spectrum of the background is correlated with the modeled zodiacal light intensity. Roughly half of the measured white noise is correlated with the zodiacal light, but a more detailed interpretation of the white noise is hampered by systematic uncertainties that are evident in the zodiacal light model. At large angular scales ($\gtrsim100"$) where excess power above the white noise is observed, we find no correlation of the power with the modeled intensity of the zodiacal light. This test clearly indicates that the large scale power in the infrared background is not being caused by the zodiacal light.