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26th of September 2017
VLBI images of active galactic nuclei
(by Müller et al.)
TANAMI (Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry) is a multiwavelength project to monitor relativistic jets in active galactic nuclei (AGN) of the Southern Sky. The team's second paper, containing high angular resolution images of the centres of 39 active galaxies, has recently been accepted for publication. The 8.4 GHz Very Long Baseline Interferometry (VLBI) image above is of the active galaxy PMN J0718−4319 (also known by its B1950 coordinates as 0717-432). No redshift has been determined for this object, so its distance is unknown. Like yesterday's galaxy, PMN J0718-4319 has a one-sided jet emerging from the bright core in the centre of the image, but in this instance the jet appears to bend significantly. In reality, it is unlikely that the bend is as pronounced as it appears in this image. The fact the jet appears one-sided strongly suggests the jet we see is directed close to our line of sight and the emission is Doppler boosted. In this case, a small change in the direction of the jet is exaggerated, as we are seeing a three-dimensional structure projected onto the two-dimensional plane of the sky. Such bends are also seen VLBI images of other active galaxies, but their origin is difficult to determine. It may be that the jet is deflected by interacting with material in the galaxy, or alternatively that the jet axis itself is precessing (in a manner analogous to a spinning top). Observations over a number of years, tracking the individual components in the jet, would help discriminate between these two options.

More details are given in the pre-print of the paper by Müller et al.

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