C.L. Carilli 1, R. Perley 1, P. van der Werf 2, G. Miley 2, & D. Harris 3
1 NRAO
2 Leiden Sterrewacht
3 SAO
At z=0.057, Cygnus A is by far the closest of the ultraluminous radio galaxies. We have undertaken an extensive study of Cygnus A in the radio, infrared, optical, and X-ray to test many aspects of jet theory for powering such sources. I will present ISO imaging of Cygnus A at 15 and 90 microns. These observations were designed to delineate the regions of the most active particle acceleration. The ISO data are the final piece in the puzzle, allowing for a fully constrained model for particle acceleration plus radiative loss mechanisms in the hot spots. I will derive accurate values of the physical parameters in the hot spots, such as the terminal jet shock width, jet inflow and outflow velocities, magnetic field strengths, hot spot pressures, and source advance speeds. The ISO images will also be used to study: (i) dust emission from the optical line emitting filaments associated with the parent cD galaxy of Cygnus A, (ii) dust emission from other galaxies in the Cygnus A cluster, and (iii) the spectrum of the active nucleus.
At 3.5 Mpc, Centaurus A is the closest of the low luminosity radio galaxies, and hence, like Cygnus A, provides an ideal opportunity to study the physical processes in the jets and parent galaxies of these low luminosity sources in unprecedented detail. Centaurus A is famous for a series of emission line filaments oriented along the axis of the radio jet. Such aligned optical line and radio emission is a common phenomenon in powerful radio galaxies at high redshift, and insight into the origin and ionization mechanism for this aligned gas provides important insight into the gaseous, and perhaps stellar, evolution of giant elliptical galaxies. Also, Centaurus A is one of the archetype optical `shell' galaxies, and recent HI 21cm imaging of Centaurus A has revealed neutral atomic gas associated with the shells. Optical shells are thought to be remnants of galaxy mergers, however detecting gas in the shells has complicated such models. We have obtained ISO observations of Centaurus A to study the dust associated with the optical line emitting filaments, and possibly with the optical and HI shells. Detecting dust emission from these regions, and determining the dust temperature, constrains models on the origin of the gas in these features, and on the ionization mechanism in the line filaments, and the radiation field and dust-to-gas ratio in the HI shells. Our ISO observations were also designed to image a large enough area to study the outer regions of the optical dust lane of the Centaurus A galaxy.