Measuring the Cosmic Infrared Background in the Near/Mid-Infrared using the Galilean Satellites as Occulters
Abstract
The Cosmic Infrared Background (CIB) contains the integrated history of the early universe, and determining its absolute value places constraints on its formation history. Measurement of the absolute value of the CIB is difficult due to contamination, most notably by the zodiacal background, e.g. sunlight scattered off small particles in the solar system. This background is the dominant signal in the mid-infrared, and dwarfs the CIB in observations made either on Earth or from spacecraft at similar distances from the sun. We have instead proposed an alternate method for measuring the CIB free of any uncertainties in the modeling of the zodiacal light. Specifically, Jupiter lies outside the bulk of the scatterers that make up the zodiacal background. The Galilean satellites normally shine by reflected sunlight, but fall dark when eclipsed by Jupiter and occult the CIB behind them. The difference between their darkened disks and the adjacent sky is a direct measurement of the absolute brightness of the CIB, independent of the zodiacal background or detector effects like floating biases. We carried out such measurements in the near- and mid-infrared using HST, Spitzer, and Subaru. The observations were extremely challenging, particularly given the extremely high level of (local to the telescope) scattered light from Jupiter. We have found that the moons are never truly dark even when eclipsed, particularly at near-IR wavelengths. We present several possible explanations for this, although we consider the most likely to be forward scattering of sunlight through the Jovian atmosphere.
- Publication:
-
IAU General Assembly
- Pub Date:
- August 2015
- Bibcode:
- 2015IAUGA..2255856S