Senior Lecturer in Radio Astronomy
"DRAGNs are relativity in action"
Active galactic nuclei are powered by accretion of material onto the supermassive black holes, massing millions to billions of suns, that lurk at the heart of large galaxies. Although the major outbursts (quasars and radio galaxies) are relatively brief episodes in the life of a galaxy, low-level activity persists in the heart of many galaxies, including our own.
With the exception of dwarfs, all galaxies have the potential to be active and almost certainly went through a period of intense activity at the time when the central bulge and associated black hole were being formed. But only about 10% of local galaxies are classed as active, though the percentage increases as we look to higher redshifts.
Activity is a somewhat slippery concept but is most easily defined as emission resulting from accretion of matter on to the black hole at the centre of a galaxy. Observationally, this activity can manifest itself in the form of Seyfert-like behaviour, ie, re-processed radiation from the accretion disk including strong, broad, high ionisation emission lines and strong blue/UV continuum emission, or as radio emission powered by jet of relativistic particles which can occur either with or without associated Seyfert-like behaviour. The range of optical luminosities can be enormous ranging from LINERS (poor cousins of Seyferts) to quasars which are the most luminous objects in the Universe. The same is true for the radio emission; the most luminous radio sources are usually accompanied by strong optical activity but the converse is not true. There really do seem to be two types of AGN, with 'radio loud' AGN producing jets about 1000 times stronger than 'radio quiet' ones, relative to the thermal radiation from the accretion disk.
Most of the research at JBCA focuses on the radio loud objects but even amongst those there is a vast range of luminosities.
Some of the key questions are:
Exciting times are ahead for AGN science: new radio facilities like e-MERLIN, EVLA, SCUBA2 and ALMA are about to come on line and there is a flood of multi-wavelength data from optical/IR/Gamma-ray surveys like SDSS, UKIDDS, Herschel GLAST.