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The evolution of radio galaxies

The evolution of radio galaxies
The evolution of radio galaxies
Radio galaxies with extended lobes are believed to interact strongly with their environment. In this thesis, I investigate the evolution of radio galaxies with different properties and track them through the cosmological ages.

In Chapters 2 and 3, I perform a ”Monte-Carlo-based” population synthesis study which combines a model for the luminosity evolution of an individual FRII source with the radio luminosity function as a function of redshift. The artificial samples generated are then compared with complete observational samples. The results show that the properties of FRII sources are required to evolve with redshift. I also study the distribution of the jet properties as a function of redshift. From currently available data it is not possible to constrain the shape of the distribution of environment density or age, but jet power is found to follow a power-law distribution with an exponent of approximately -2. This power-law slope does not change with redshift out to z = 0.6. I also find the distribution of the pressure in the lobes of FRII sources to evolve with redshift up to z ~ 1.2.

FRI sources are not yet considered in Chapter 3, as existing analytical models for FRI soures are less successful. Thus in Chapters 4, I present a new analytical model for FRI jets. The model is based on a mixing-layer structure in which an initially laminar, relativistic flow is surrounded by a shear layer. I apply the appropriate conservation laws to constrain the jet parameters, starting the model where the radio emission is observed to brighten abruptly. Applying the model to a sample of the well-observed FRI sources, including example 3C 31, I find a self-consistent solution, from which I derive the jet power together with other properties like the entrainment rate.

The model in Chapter 4 leads an idea of estimating the maximum lengths and ages of the FR II sources by considering the entrainment process during their evolutions. In Chapter 5, I consider the laminar part of the jet may be destroyed due to the entrainment under certain assumpsions, in which case the radio outflows cease to be FR IIs after a few 108 yrs, at which point they have typically reached sizes of around 1 Mpc. Based on this idea, I then further discuss a plausible transition process from FRIIs into FRIs.
Wang, Yang
c56a6976-ef90-42bf-a8bc-9f227aa211bd
Wang, Yang
c56a6976-ef90-42bf-a8bc-9f227aa211bd
Knigge, Christian
ac320eec-631a-426e-b2db-717c8bf7857e

Wang, Yang (2010) The evolution of radio galaxies. University of Southampton, School of Physics and Astronomy, Doctoral Thesis, 155pp.

Record type: Thesis (Doctoral)

Abstract

Radio galaxies with extended lobes are believed to interact strongly with their environment. In this thesis, I investigate the evolution of radio galaxies with different properties and track them through the cosmological ages.

In Chapters 2 and 3, I perform a ”Monte-Carlo-based” population synthesis study which combines a model for the luminosity evolution of an individual FRII source with the radio luminosity function as a function of redshift. The artificial samples generated are then compared with complete observational samples. The results show that the properties of FRII sources are required to evolve with redshift. I also study the distribution of the jet properties as a function of redshift. From currently available data it is not possible to constrain the shape of the distribution of environment density or age, but jet power is found to follow a power-law distribution with an exponent of approximately -2. This power-law slope does not change with redshift out to z = 0.6. I also find the distribution of the pressure in the lobes of FRII sources to evolve with redshift up to z ~ 1.2.

FRI sources are not yet considered in Chapter 3, as existing analytical models for FRI soures are less successful. Thus in Chapters 4, I present a new analytical model for FRI jets. The model is based on a mixing-layer structure in which an initially laminar, relativistic flow is surrounded by a shear layer. I apply the appropriate conservation laws to constrain the jet parameters, starting the model where the radio emission is observed to brighten abruptly. Applying the model to a sample of the well-observed FRI sources, including example 3C 31, I find a self-consistent solution, from which I derive the jet power together with other properties like the entrainment rate.

The model in Chapter 4 leads an idea of estimating the maximum lengths and ages of the FR II sources by considering the entrainment process during their evolutions. In Chapter 5, I consider the laminar part of the jet may be destroyed due to the entrainment under certain assumpsions, in which case the radio outflows cease to be FR IIs after a few 108 yrs, at which point they have typically reached sizes of around 1 Mpc. Based on this idea, I then further discuss a plausible transition process from FRIIs into FRIs.

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Published date: 28 February 2010
Organisations: University of Southampton

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Local EPrints ID: 161183
URI: http://eprints.soton.ac.uk/id/eprint/161183
PURE UUID: 4b8c2826-8760-4cb8-b781-977804989a5a

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Date deposited: 30 Jul 2010 11:37
Last modified: 14 Mar 2024 01:59

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Contributors

Author: Yang Wang
Thesis advisor: Christian Knigge

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