Flickering Faint Galaxies: Few and Far Between
  Optical variability in galaxies at high redshift is a tracer of evolution in AGN activity, and should provide a useful constraint on models of galaxy evolution, AGN structure, and cosmology. We studied optical variability in multiple deep CCD and photographic surveys of blank fields for galaxies with $B_j = 20 - 25$ mag. Weakly variable objects are far more common than strongly variable ones. For objects near $B_j = 22$, $0.74\% \pm 0.2 \%$ vary by 0.026~mag RMS or more, over a decade. This is small compared with previous claims based on photographic surveys, and also small compared with the fraction of bright quasars ($\approx 5\%$ at $B_j = 20$~mag) or Seyferts ($\approx 1-2\%$ for $B_j < 18$). The fraction of objects that vary increases slowly with magnitude. Detection probabilities and error rates were checked by simulations and statistical analysis of fluctuations of sample sky spots. 
Greg P. Kochanski, J. Anthony Tyson, Philippe Fischer