A Spitzer IRAC Measure of the Zodiacal Light

TL;DR

This study uses Spitzer IRAC data collected over 8.5 years to measure zodiacal light variations, compare them with existing models, and identify discrepancies that can improve understanding of interplanetary dust distribution.

Contribution

The paper provides long-term IRAC measurements of zodiacal light, revealing discrepancies with existing models and suggesting potential dust disk warping and overdensities.

Findings

Measured zodiacal light variation over 8.5 years

Identified a few percent discrepancy with Kelsall et al. (1998) model

Detected potential warping and overdensity in the dust disk

Abstract

The dominant non-instrumental background source for space-based infrared observatories is the zo- diacal light. We present Spitzer Infrared Array Camera (IRAC) measurements of the zodiacal light at 3.6, 4.5, 5.8, and 8.0 {\mu}m, taken as part of the instrument calibrations. We measure the changing surface brightness levels in approximately weekly IRAC observations near the north ecliptic pole (NEP) over the period of roughly 8.5 years. This long time baseline is crucial for measuring the annual sinusoidal variation in the signal levels due to the tilt of the dust disk with respect to the ecliptic, which is the true signal of the zodiacal light. This is compared to both Cosmic Background Explorer Diffuse Infrared Background Experiment (COBE DIRBE) data and a zodiacal light model based thereon. Our data show a few percent discrepancy from the Kelsall et al. (1998) model including a potential warping of the interplanetary dust disk and a previously detected overdensity in the dust cloud directly behind the Earth in its orbit. Accurate knowledge of the zodiacal light is important for both extragalactic and Galactic astronomy including measurements of the cosmic infrared background, absolute measures of extended sources, and comparison to extrasolar interplanetary dust models. IRAC data can be used to further inform and test future zodiacal light models.