Constraints on Galaxy Formation from Deep Galaxy Redshift Surveys and   Quasar Absorption Line Studies
  Magnitude-limited galaxy redshift surveys are now providing large samples of galaxies to beyond z=2, while color-selected and emission-line-selected samples are finding galaxies to z=4.7. A broad picture is emerging of galaxy formation peaking in the z=1 range, which ties in with the metallicity and density evolution seen in the quasar absorption lines. We still have no direct information beyond z=5, but the ionization of the IGM at this redshift argues for activity prior to this time. The metallicities of around 0.01 solar which appear to be relatively ubiquitous in quasar absorption lines beyond z=2, even in very low column density clouds, could be a relict of this period. 
Lennox L. Cowie