A Caltech Library Service

Cosmic Distribution of Optically Selected Quasars

Schmidt, Maarten (1987) Cosmic Distribution of Optically Selected Quasars. In: Observational Cosmology. International Astronomical Union Symposium (IAUS). No.124. Springer Netherlands , Dordrecht, pp. 619-625. ISBN 9789027724762.

Full text is not posted in this repository. Consult Related URLs below.

Use this Persistent URL to link to this item:


Counts of optically selected quasars as a function of magnitude and redshift show the effects of strong evolution. If quasars have relatively short life times, then the observed numbers at a given redshift are mostly determined by their birth rate and mean luminosity over their lifetime. In this case the evolution of the luminosity function can be described by density evolution, where the rate of evolution may depend on luminosity and other properties. On the other hand, if all quasars were formed at large redshift and have been decaying in luminosity since that time, then the evolution of the luminosity function is best described in terms of luminosity evolution. We discuss some of the consequences of luminosity evolution for the mass of quasars and for the X-ray background. We explore the observational aspects of the redshift cutoff of quasars. The situation is complicated by the unavoidable bias in slitless surveys against weak-line objects. Since quasar emission lines show a wide range of equivalent widths, a spectral survey will be characterized by a distribution of limiting continuum magnitudes rather than by a single value. The decline in the space density of quasars at large redshift may depend on luminosity, and may also have structure, such as a steep drop, but not a total cutoff, in density at a redshift near 3.

Item Type:Book Section
Related URLs:
URLURL TypeDescription ReadCube access
Additional Information:© IAU 1987. This research was supported in part by the National Science Foundation under grant AST-8314134.
Funding AgencyGrant Number
Subject Keywords:Light Curve; Radio Source; Equivalent Width; Luminosity Function; Large Redshift
Series Name:International Astronomical Union Symposium (IAUS)
Issue or Number:124
Record Number:CaltechAUTHORS:20200930-113054010
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105671
Deposited By: George Porter
Deposited On:30 Sep 2020 22:31
Last Modified:16 Nov 2021 18:45

Repository Staff Only: item control page