The interface between radio jets and ionized gas clouds
ASTR SOC P 250 (2002) 467-470
Abstract:
Optical spectra of the narrow, disturbed, interface regions between radio jets and gas clouds in the interstellar medium of the host galaxies of two nearby radio sources have diagnostic (BPT) diagrams for line ratios of [NII], [OIII], [SII], Halpha and Hbeta which are inconsistent with published models for shock heating, as well as those for photoionization/excitation by either a "hard" continuum or flux from ordinary hot stars. This may indicate the need for additional work on these models or it may indicate that the ionized gas in the jet/cloud interface has an energy distribution which is partly characterised by that in the radio jet plasma itself If the latter is correct, then careful measurements of these interface regions may allow us to distinguish between beams of particles composed of electrons and positrons and those composed of electrons and protons.The large-scale structure of 3C 31
ASTR SOC P 250 (2002) 437-442
Abstract:
The results of a multifrequency VLA imaging study of the nearby radio galaxy 3C 31 are briefly summarized. The transition between jets and lobes is much more complex than was apparent from earlier observations, and is associated with significant variations in spectral index. We demonstrate that the known depolarization asymmetry in 3C 31 is caused by foreground Faraday rotation in the halo of the host galaxy, but the details of the associated field and density structure are not yet clear.The nature of jets: evidence from circular polarization observations
ASTR SOC P 250 (2002) 152-163
Abstract:
We review recent observations of circularly polarized radiation from AGN made with the VLBA and with the ATCA. We also discuss briefly the detections of the Galactic sources Sgr A* and SS 433. The origin of the circular polarization is still an open question in most cases, and we discuss four possible mechanisms. Detectable circular polarization is a common property of quasars, but not of radio galaxies, and is always associated with the compact core. There is growing evidence that the sign of the circular polarization stays the same over at least 20 - 30 years, suggesting that it is a fundamental property of the jet.The origin of ultra high energy cosmic rays: where we are now and what the future holds
ASTR SOC P 250 (2002) 117-122
Abstract:
The observational picture for cosmic rays above 10(19) eV is described and the enigma that these results pose is discussed. The existence of particles above 10(20) eV may have an impact on our understanding of magnetic fields in intergalactic space and in possible sources.The parsec-scale central components of FRI radio galaxies
ASTR SOC P 250 (2002) 100-103