Spectrophotometric measurement of the Extragalacic Background Light
  The Extragalactic Background Light (EBL) at UV, optical and NIR wavelengths
consists of the integrated light of all unresolved galaxies along the line of
sight plus any contributions by intergalactic matter including hypothetical
decaying relic particles. The measurement of the EBL has turned out to be a
tedious problem. This is because of the foreground components of the night sky
brightness, much larger than the EBL itself: the Zodiacal Light (ZL),
Integrated Starlight (ISL), Diffuse Galactic Light (DGL) and, for ground-based
observations, the Airglow (AGL) and the tropospheric scattered light. We have
been developing a method for the EBL measurement which utilises the screening
effect of a dark nebula on the EBL. A differential measurement in the direction
of a high-latitude dark nebula and its surrounding area provides a signal that
is due to two components only, i.e. the EBL and the diffusely scattered ISL
from the cloud. We present a progress report of this method where we are now
utilising intermediate resolution spectroscopy with ESO's VLT telescope. We
detect and remove the scattered ISL component by using its characteristic
Fraunhofer line spectral signature. In contrast to the ISL, in the EBL spectrum
all spectral lines are washed out. We present a high quality spectrum
representing the difference between an opaque position within our target cloud
and several clear OFF positions around the cloud. We derive a preliminary EBL
value at 400 nm and an upper limit to the EBL at 520 nm. These values are in
the same range as the EBL lower limits derived from galaxy counts.
