Characterizing the red optical sky background fluctuations from
  narrow-band imaging
  The detection and characterization of the physical properties of very distant
galaxies will be one the prominent science case of all future Extremely Large
Telescopes, including the 39m E-ELT. Multi-Object Spectroscopic instruments are
potentially very important tools for studying these objects, and in particular
fiber-based concepts. However, detecting and studying such faint and distant
sources will require subtraction of the sky background signal (i.e., between OH
airglow lines) with an accuracy of ~1%. This requires a precise and accurate
knowledge of the sky background temporal and spatial fluctuations. Using FORS2
narrow-band filter imaging data, we are currently investigating what are the
fluctuations of the sky background at ~9000A. We present preliminary results of
sky background fluctuations from this study over spatial scales reaching ~4
arcmin, as well as first glimpses into the temporal variations of such
fluctuations over timescales of the order of the hour. This study (and other
complementary on-going studies) will be essential in designing the
next-generation fiber-fed instruments for the E-ELT.
