(Proposal ID) S14A-080

(PI) Tsumura Kohji

(Proposal Title)
 Multi-band measurement of extragalactic background light by Callisto eclipses

(Abstract)
The Extragalactic Background Light (EBL) as an integrated history of the early 
universe is important for the study of the Dark Ages, and it may include the 
light from the first stars at z~10. However, previous EBL measurements suffer 
from residual contamination from strong foreground emission (e.g. the zodiacal 
light). We have conducted the EBL observations using the occulting method by 
Galilean satellites (Europa and Ganymede) in eclipse at near-infrared 
wavelengths. This method allows us to measure the absolute EBL brightness 
with no zodiacal light uncertainty. However, owing to strong stray light due 
to the close proximity of Jupiter, these measurements have been limited at the 
CH4-long band where Jupiter is significantly dark thanks to CH4 absorption in 
the Jovian atmosphere. Following the success of these observations, we propose 
to use Callisto in eclipse as an occulter for multi-band EBL measurement. 
Because Callisto eclipses occur much farther (>60 arcsec from Jovian limb) 
than Europa (<30 arcsec) and Ganymede (<60 arcsec) eclipses, and we confirmed 
that stray light from Jupiter at >50 arcsec can be negligible even at J and H 
bands, multi-band EBL measurement around its spectral peak (J-band) can be 
achieved only by the Callisto eclipse occultation.