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Cavendish Astrophysics
Cavendish Laboratory

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Science Programme
Regulating the ISM and star formation
Cosmological evolution of star-forming galaxies
The origin and evolution of radio sources
Radio sources and their environments
Micro quasars


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Paul Alexander

Cavendish Astrophysics

Galaxy Evolution

Radio Sources and their Environments

As radio sources evolve they strongly interact with their environment.  We are investigating how this interaction effects galaxy evolution in general as well as the feedback effect of the radio source on its host galaxy and AGN.

Composite image showing the extended optical emission associated with 3CXXX.  The false-colour image is of an HST observation and the contours show the radio source. 

One direct observational manifestation of this interaction is the existence of extended regions of emission-line gas which show a clear spatial relationship to the radio source itself.  This extended emission shows evidence of both shock excitation and excitation by the AGN itself.

Direct evidence for radio-source induced star-formation may have been recently detected at z ~ 1 in our HST imaging of at least one 6C radio source.

To investigate the comological evolution of this interaction we are working on a comparison of our 3CR sample and a sample of 6C radio galaxies at z~1 using HST imaging, UKIRT JHK imaging, WHT Isis spectroscopy as well as radio studies.   We are able to compare directly objects matched in power but at different redshift as well as objects of different power at the same redshift thus breaking the P-z degeneracy.   

Results of a simulation showing the gas density as a two-jet radio source propagates into a realistic cluster atmosphere which has a pre-existing cooling flow.   A video of this simulation is also available showing density and temperature evolution.

We are modelling the interaction of the radio sources with their environments using analytical and computational techniques. The aim is to obtain an understanding of the effect of the effect of the radio source on the intracluster gas and feedback processes on the AGN itself.  Simulations and analytical modelling of the passage of a radio source through a clumpy inhomogeneous medium are being used to help understand our observational work on the extended emission-line gas.

The 3D numerical hydrodynamic simulations are performed using the ZEUS code (a computational fluid dynamics code developed at the Laboratory for Computational Astrophysics at the NCSA) and run on our local Beowulf cluster.

University of Cambridge    Last modified: 20/1/2002