Active Galaxies

A number of theme members are involved in the study of active galactic nuclei (AGN), particularly radio galaxies, using radio, infra-red, optical, and X-ray techniques. Interests include the environments and dynamics of radio sources, unified models for both high-power and low-power objects, observation and modelling of jets and the X-ray/radio relationship in radio galaxies and quasars. Instruments used by the theme include the VLA, the VLBAMERLIN, the ATCABIMAISO, the HSTROSATASCAXMM and Chandra.

Active galaxies can also be used as cosmological probes. Powerful radio sources are markers of massive structures (clusters of galaxies); by observing them at high redshift we can find massive structures in the early universe, which allows us to test models of structure formation, a key goal of cosmology. Once these structures are found, multi-waveband observations are being used to determine key parameters such as mass, dynamical state and baryon content. Radio observations (e.g. of the Sunyaev-Zel'dovich effect), optical (peculiar velocities, weak lensing) and X-ray observations (measurement of the hot intracluster plasma properties) all contribute to these studies.

Figure 1 shows the radio galaxy Centaurus A. The red colours come from an image at radio frequencies, made with the Very Large Array in New Mexico. The blue colours are from an X-ray image made with the orbiting X-ray telescope Chandra. The core of the galaxy is at the bottom right: the jet extends across to the upper left.

Plasma Processes

Many of the observable properties of active galaxies are related to plasma processes in the sources, and these relate to terrestrial fusion plasma physics. Work in the group on particle acceleration and radiation has led to collaborations with the UKAEA fusion physics research group at Culham, and suggests future lines of research with the coming generation of radio telescopes, such as the SKA.


Fig. 1. Central regions of the radio galaxy Centaurus A
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