Mining for Metals in the Lyman Alpha Forest
  In order to ascertain the extent of metal enrichment in the Ly alpha forest, we have analysed a very high S/N spectrum of the z = 3.625 QSO Q1422+231. We find that in high column density Ly alpha clouds, the power law column density distribution function of C IV continues down to log N(C IV) = 11.7. In addition, by analysing pixel-by-pixel optical depths we show that there are considerably more metals in the Ly alpha forest than are currently directly detectable. 
Sara L. Ellison, Antoinette Songaila, Joop Schaye, Max Pettini