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Modelling the Quasar Luminosity Function in Hierarchical Models for Structure Formation

from II - Luminosity Functions and Continuum Energy Distributions

Published online by Cambridge University Press:  04 August 2010

Martin Haehnelt
Affiliation:
Institute of Astronomy, Madingley Road, Cambridge CB3 0HA
Andrew Robinson
Affiliation:
University of Cambridge
Roberto Juan Terlevich
Affiliation:
Royal Greenwich Observatory, Cambridge
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Summary

Abstract

The strong evolution of the host object population postulated in hierarchical models for structure formation is invoked to explain the observed strong evolution of the space density of quasars. The quasar activity is interpreted as marking the advent of a new step in the hierarchic build-up of bigger and bigger dark matter halos. The Press–Schechter formalism within the CDM scenario is used to estimate the number of newly forming dark matter halos. Pronounced peaks are found in the number density of newly forming massive black holes, capable of explaining the short time scale of the evolution of the quasar population. A gratifying fit to the observed luminosity function is obtained.

Quasar evolution in the CDM scenario

Soon after the discovery of the first quasars it was noticed that quasars are a strongly evolving population of objects. With the increasing number of known intermediate redshift quasars it became possible to determine the time evolution of the luminosity function of quasars. The main feature of the luminosity function is a characteristic break luminosity which decreases with time. The quasar luminosity function is most naturally interpreted as a superposition of many generations of short-lived quasars with a life time ∼ 108yr and a characteristic mass that decreases with time as ∼ (1 + z)3.

In hierarchical models for structure formation, such as the CDM scenario, larger and larger structures build up by merging of smaller structures and the smaller structures are at least partially erased.

Type
Chapter
Information
The Nature of Compact Objects in Active Galactic Nuclei
Proceedings of the 33rd Herstmonceux Conference, held in Cambridge, July 6-22, 1992
, pp. 123 - 124
Publisher: Cambridge University Press
Print publication year: 1994

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