(Proposal ID) S12A-022

(PI) Tsumura, Kohji

(Proposal Title)
Cosmic Infrared Background by Eclipsed Galilean Satellites Shielding

(Abstract)
Observation of the Cosmic Infrared Background (CIB) as an accumulated history 
of the early universe is important for the study of the Dark Age, and it may 
includes the light from the first stars at z~10. However previous CIB 
measurements were suffered from the strong foregrounds especially the zodiacal 
light (ZL). We propose to observe the eclipsed Galilean satellites in the 
Jovian shadow to detect the absolute CIB intensity without any ZL subtraction 
error. Since the eclipsed Galilean satellite shields all light beyond the 
Jovian orbit, it should be detected as a "dark spot" if strong CIB exists as 
previous observations imply. Measurement of this darkness allows us to set the 
lower limit of CIB without the ZL subtraction error because ZL is common to 
both the eclipsed satellite and the sky around it, therefore ZL will be 
eliminated by differencing them.  Estimated darkness magnitude is 23.0 
(Ganymede) or 24.1 (Europa) Vega magnitude in J-band, which can be detected 
with IRCS by 1 or 2 hour integration with 5 sigma respectively.