The e-MERLIN Legacy programme
Resolving Key Questions in Extragalactic Jet Physics
Robert Laing (ESO, Garching, Germany) and Martin Hardcastle (Hertfordshire)
P. Alexander (Cavendish Laboratory, Cambridge, UK), M. Birkinshaw (University of Bristol, UK), A.H. Bridle (NRAO, USA), I.W.A. Browne (JBCA, University of Manchester, UK), W.D. Cotton (NRAO, USA), J.H. Croston (University of Hertfordshire, UK), F. Dulwich (University of Oxford, UK), D.A. Evans (Harvard/CfA, USA), D. Gabuzda (University College Cork, Ireland), S. Garrington (JBCA, University of Manchester, UK) D. Guidetti (INAF - IRA, Bologna/ESO, Italy) M.J. Hardcastle (University of Hertfordshire, UK) R.A. Laing (ESO), J.P. Leahy (JBCA, University of Manchester, UK), R. Morganti (ASTRON, The Netherlands), P. Parma (INAF - IRA, Bologna, Italy), J.M. Riley (Cavendish Laboratory, Cambridge, UK), D.M. Worrall (University of Bristol, UK)
We propose to image a carefully selected sample of bright, extragalactic radio sources with e-MERLIN at L and C bands to provide a legacy data set for jet physics. It is now well established that jets, on all scales, are a key astrophysical phenomenon, and in addition they provide a mechanism for coupling the output of AGN to their largescale surroundings. Our overarching aim is to measure the physical properties of extragalactic jets: these are key ingredients in understanding the r?e of radio sources in the evolution of structure in the Universe and the production of high-energy cosmic rays. Our primary science questions include:
1. What are the dynamics of radio jets in the vicinity of the AGN? How are low-luminosity radio jets decelerated on sub-kpc scales? What are the jet velocities, magnetic-field structures, powers, mass fluxes and entrainment rates? The key new aspect of the e-MERLIN observations is the ability to resolve the jets where they first brighten.
2. What are the three-dimensional structures of powerful jets? Do they have highly relativistic ?spines?? e-MERLIN will allow transverse resolution of the jets with good sensitivity for the first time.
3. What are the magnetic field configurations immediately surrounding jets? Is there evidence for confining fields? e-MERLIN will be able to determine Faraday rotation measures within a single observing band at high spatial resolution.
4. Where and how are particles accelerated in the hot-spots and jets of powerful sources? By allowing us to measure synchrotron spectra and polarization in many discrete regions across these kpc-scale regions, e-MERLIN will enable studies of their electron populations and magnetic field sub-structures.
We will select the brightest few representative examples of distinct types of source from well-defined samples limited by flux density and redshift and observe them with high sensitivity and image fidelity. Our targets are the defining members of their classes, and include famous objects such as Cygnus A, M87 and 3C 273. Without exception, they have a wealth of data available at radio and other wavelengths, and the new observations will have enduring legacy value.