The Quasar Redshift Cut-Off

  • Richard F. Green
Part of the NATO ASI Series book series (ASIC, volume 264)

Abstract

Evidence for a cut-off in the comoving density of quasars at z>2.5 is examined. The basis for comparison is the luminosity function of quasars at lower redshifts, which is becoming increasingly well determined. The change of the LF with cosmic time can be parameterized by luminosity evolution or luminosity-dependent density evolution. New complete surveys for high-redshift quasars by slit less spectroscopy and color selection indicate the presence of a strong peak in the integrated density of luminous quasars near z=2. The question is whether the deficit of high-redshift quasars reflects the true distribution, consistent with the results from radio source counts, of whether it is apparent because of increasing obscuration by intervening dust. The damped Lyman α systems alone cannot produce the observed decrease. A simple exercise shows that optically thick systems with column densities down to log N (H I) = 19.7 and Galactic dust/neutral gas ratios can reproduce the observations for a population of high-redshift quasars as numerous as that at z=2, provided the dust has a very weak 2200 Å feature. Physical consequences of various scenarios are discussed.

Keywords

Column Density Cosmic Time High Redshift Luminosity Function Lower Redshift 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Kluwer Academic Publishers 1989

Authors and Affiliations

  • Richard F. Green
    • 1
  1. 1.Kitt Peak National ObservatoryNational Optical Astronomy ObservatoriesTucsonUSA

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