Cosmological Evolution of Quasars

Abstract

We present a model for the cosmological evolution of quasars (QSOs) under the assumption that they are powered by massive accreting black holes. Accretion flows around massive black holes make a transition from high radiative efficiency ($\sim 10$) to low efficiency, advection-dominated flows when $\dot{M}/{\dot{M}}_{Edd}$ falls below the critical rate $\sim 0.3{\alpha }^2\sim 10^{-2}$ where $\dot{M}$ is the mass accretion rate, ${\dot{M}}_{Edd}\propto M$ is the usual Eddington rate with the nominal 10% efficiency, and $\alpha (\le 1)$ is the dimensionless viscosity parameter. We identify this transition with the observed break at a redshift $\sim 2$ in the QSOs' X-ray luminosity evolution. Growth of black holes through accretion could naturally lead to such a transition at a critical redshift $z_c\sim 1-3$, provided that most of high redshift QSOs appear with near Eddington luminosities at $z\sim 3-4$ and the accretion rates decline over the Hubble time in a roughly synchronous manner. Before the transition, the QSOs' luminosities (with a high efficiency) slowly decrease and after the transition at $z_c$, the QSO luminosities evolve approximately as $\propto (1+z{)}^{K(z)}$ where $K(z)$ gradually varies from $z=z_c$ to $z\sim 0$ around $K\sim 3$. The results depend on the details of the QSO X-ray emission mechanism. We discuss some further implications.

Latex, 2 PS figures, To Appear in ApJ

References in corpus (2)

• Is the Accretion Flow in NGC 4258 Advection-dominated?
• The ROSAT X-ray Spectra of BL Lacertae Objects

Cited by in corpus (16)

• Advection-Dominated Accretion Model of the Black Hole V404 Cyg in Quiescence
• Early Growth and Efficient Accretion of Massive Black Holes at High Redshift
• Fuelling quasars with hot gas
• On the Cosmological Evolution of the Luminosity Function and the Accretion Rate of Quasars
• Deriving the Quasar Luminosity Function from Accretion Disk Instabilities
• Quasars and galaxy formation
• Preheated Advection Dominated Accretion Flow
• Evidence for the evolutionary sequence of blazars: different types of accretion flows in BL Lac objects
• The jet power extracted from a magnetized accretion disc
• Accretion Disk Instabilities, CDM models and their role in Quasar Evolution
• On Radio and X-ray Emission Mechanisms in Nearby, X-ray Bright Galactic Nuclei
• Constraints on radiatively inefficient accretion history from Eddington ratio distribution of active galactic nuclei
• Theoretical Models of Multi-waveband QSO Luminosity Functions
• A Morphological and Multicolor Survey for Faint QSOs in the Groth-Westphal Strip
• Cosmological Luminosity Evolution of QSO/AGN Population
• Cosmological Evolution Models for QSO/AGN Luminosity Functions: Effects of Spectrum-Luminosity Correlation and Massive Black Hole Remnants