Probing the innermost regions of AGN jets and their magnetic fields with RadioAstron

Probing the innermost regions of AGN jets and their magnetic fields with RadioAstron: IV. The quasar 3C 345 at 18 cm: Magnetic field structure and brightness temperature

Potzl, F. M. (Max-Planck-Institute for Radio Astronomy)
Lobanov, A. P. (Max-Planck-Institute for Radio Astronomy; Moscow Institute of Physics and Technology)
Gomez, J. L. (Instituto de Astrofísica de Andalucía-Consejo Superior de Investigaciones Científicas (CSIC))
Bach, U. (Max-Planck-Institute for Radio Astronomy)
Fuentes, A. (Instituto de Astrofísica de Andalucía-Consejo Superior de Investigaciones Científicas (CSIC))
Gurvits, L. (TU Delft Astrodynamics & Space Missions; Joint Institute for VLBI ERIC; Oceans and Atmosphere)
Jauncey, D. L. (Oceans and Atmosphere; Australian National University)
Kovalev, Y. Y. (Max-Planck-Institute for Radio Astronomy; Moscow Institute of Physics and Technology; Russian Academy of Sciences)
Kravchenko, E. V. (Moscow Institute of Physics and Technology; Russian Academy of Sciences; INAF Istituto di Radioastronomia)

2021

Context. Supermassive black holes in the centres of radio-loud active galactic nuclei (AGN) can produce collimated relativistic outflows (jets). Magnetic fields are thought to play a key role in the formation and collimation of these jets, but the details are much debated. Aims. We study the innermost jet morphology and magnetic field strength in the AGN 3C 345 with an unprecedented resolution using images obtained within the framework of the key science programme on AGN polarisation of the Space VLBI mission RadioAstron. Methods. We observed the flat spectrum radio quasar 3C 345 at 1.6 GHz on 2016 March 30 with RadioAstron and 18 ground-based radio telescopes in full polarisation mode. Results. Our images, in both total intensity and linear polarisation, reveal a complex jet structure at 300 μas angular resolution, corresponding to a projected linear scale of about 2 pc or a few thousand gravitational radii. We identify the synchrotron self-absorbed core at the jet base and find the brightest feature in the jet 1.5 mas downstream of the core. Several polarised components appear in the Space VLBI images that cannot be seen from ground array-only images. Except for the core, the electric vector position angles follow the local jet direction, suggesting a magnetic field perpendicular to the jet. This indicates the presence of plane perpendicular shocks in these regions. Additionally, we infer a minimum brightness temperature at the largest (u,  v)-distances of 1.1  ×  1012 K in the source frame, which is above the inverse Compton limit and an order of magnitude larger than the equipartition value. This indicates locally efficient injection or re-acceleration of particles in the jet to counter the inverse Compton cooling or the geometry of the jet creates significant changes in the Doppler factor, which has to be > 11 to explain the high brightness temperatures.

Galaxies: active
Galaxies: jets
Galaxies: magnetic fields
Quasars: individual: 3C 345
Radio continuum: galaxies

http://resolver.tudelft.nl/uuid:54235943-0c85-44c8-a8c1-07cb1a0cf48e

https://doi.org/10.1051/0004-6361/202039493

0004-6361

Astronomy & Astrophysics, 648

Institutional Repository

journal article

© 2021 F. M. Potzl, A. P. Lobanov, J. L. Gomez, U. Bach, A. Fuentes, L. Gurvits, D. L. Jauncey, Y. Y. Kovalev, E. V. Kravchenko, More Authors