Faint Field Galaxies: A Population of Intrinsically Faint Objects at Low   Redshift?
  To distinguish between the different models proposed to understand the excess of faint field counts over the predictions from non-evolving models, a number of redshift surveys have been undertaken. The answer has not arrived yet due to the high rate of incompleteness achieved. Un-identified galaxies have been shown to be bluer than identified ones. In this paper, it is argued that some of these galaxies could be "quiescent" dwarfs, still quite blue, but with featureless spectra. 
Ana Campos (Instituto Astrofisica Andalucia Csic)