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Quasars: Their Evolution, Absorption Lines and the Intergalactic Gas

Published online by Cambridge University Press:  25 April 2016

G. Setti

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For many years now it has been known that the number vs. magnitude counts of quasars is the prima facie evidence of a cosmological evolution of this class of objects. Down to an apparent magnitude B - 19 the number of quasars increases by almost a factor 8 per magnitude Interval, compared to a factor 4 obtained in an Euclidean universe filled with a uniform distribution of sources, and correspondingly less for the classical Friedmann models of Gen. Relativity due to the red-shift effects. This strong evolution has been recently questioned because of several biases which may artificially steepen the slope of the counts in the optical surveys. Deep surveys of quasars selected via multi-colour techniques down to B - 23 have confirmed the long standing inference that the number count relationship must flatten beyond B - 20. As a consequence, pure density evolution models, where only the number density of quasars increases with the redshift z, leaving unchanged the shape of the local luminosity function, are ruled out, since too many quasars are predicted at faint magnitudes compared to the dramatic flattening of the counts (see, e.g., ref. 4).

Type
Research Article
Information
Transactions of the International Astronomical Union , Volume 20 , Issue 1 , 1988 , pp. 666 - 670
Copyright
Copyright © Kluwer 1988 

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