Quasar colors - Statistics and cosmological evolution

A model spectrum is constructed to study QSO broadband colors as a function of redshift. The available statistical data are used to generate realistic color distributions that give quantitative estimates of the incompleteness associated with the various color selection techniques as a function of redshift. Also developed is a simple model for the average Lyman-continuum absorption, based on the statistics of the Ly-alpha clouds, to explore the resulting colors of high-redshift QSOs. Selection biases on the estimate of QSO density at high redshift are also discussed. 36 refs