A Spitzer IRAC measure of the zodiacal light

Abstract

ABSTRACT The dominant non-instrumental background source for space {based infrared observatories is the zodiacal light(ZL). We present Spitzer Infrared Array Camera (IRAC) measurements of the ZL at 3.6, 4 .5, 5.8, and 8.0  m,taken as part of the instrument calibrations. We measure the changing surface brightness levels in approximatelyweekly IRAC observations near the north ecliptic pole over t he period of roughly 8.5 years. This long timebaseline is crucial for measuring the annual sinusoidal var iation in the signal levels due to the tilt of the dust diskwith respect to the ecliptic, which is the true signal of the Z L. This is compared to both Cosmic BackgroundExplorer Di use Infrared Background Experiment data and a Z L model based thereon. Our data show a fewpercent discrepancy from the Kelsall et al.(1998) 1 model including a potential warping of the interplanetary d ustdisk and a previously detected overdensity in the dust cloud directly behind the Earth in its orbit. Accurateknowledge of the ZL is important for both extragalactic and G alactic astronomy including measurements of thecosmic infrared background, absolute measures of extended sources, and comparison to extrasolar interplanetarydust models. IRAC data can be used to further inform and test f uture ZL models.Keywords: cosmology: di use radiation | interplanetary medium | infr ared: di use background