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Studying the Relativistic Jets of Active Galactic Nuclei Denise Gabuzda Radio Astronomy Group

Studying the Relativistic Jets of Active Galactic Nuclei Denise Gabuzda Radio Astronomy Group. Colm Coughlan. Fiona Healy. Eoin Murphy. Active Galactic Nuclei (AGN): extremely compact, generate much more energy than a normal galaxy.

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Studying the Relativistic Jets of Active Galactic Nuclei Denise Gabuzda Radio Astronomy Group

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  1. Studying the Relativistic Jets of Active Galactic NucleiDenise GabuzdaRadio Astronomy Group Colm Coughlan Fiona Healy Eoin Murphy

  2. Active Galactic Nuclei (AGN): extremely compact, generate much more energy than a normal galaxy. Activity due to accretion onto a supermassive (~109 solar masses! ) black hole Sometimes eject “jets” of radio-emitting plasma extending far beyond optical (visible) galaxy.

  3. This radio emission is SYNCHROTRON RADIATION — electromagetic radiation given off by energetic electrons during their acceleration by local magnetic fields.

  4. Radio Interferometry - using an array of radio telescopes with synchronized signals, provides resolution Where D is maximum distance between telescopes used. Can use different radio telescope arrays to study jets on different scales. R ~ l/D

  5. In connected-element arrays, the telescopes are linked electronically Images of AGN jets obtained with the VLA, scales of kiloparsec (1000’s of light years) Very Large Array (VLA), max baseline 36 km

  6. Very Long Baseline Array (VLBA) In Very Long Baseline Interferometry, the data are usually recorded on disc and processed after the observations

  7. Images of AGN jets obtained with the American VLBA — one-sided structure due to Doppler beaming

  8. The direction of the linear polarization is perpendicular to the B field. The linear polarization of the radio emission tells us about the B field giving rise to the synchrotron radiation. In these images, B is perpendicular to the jets.

  9. This orthogonal B field may be the toroidal component of an intrinsic underlying helical B field, due to rotation of the central supermassive black hole and its accretion disc + relativistic jet outflow. Meier, Koide & Uchida 2001

  10. Faraday rotation of the plane of polarisation occurs when an EM wave passes through a magnetised plasma, due to different propagation velocities of the RCP and LCP components of the EM wave in the plasma. The rotation is proportional to the square of the wavelength, and its sign is determined by the direction of the line-of- sight B field: • = o + RM 2 RM = (constants)  ne B•dl

  11. A helical jet B field should give rise to a gradient in the Faraday rotation across the jet, due to the systematic change in the line-of-sight component of the helical field.  LOS B away from observer (RM < 0) B Jet axis LOS B towards observer (RM > 0) •

  12. 10-credit projects (PY4115) Searching for new AGN jets displaying evidence for helical jet B fields Making and analyzing Faraday rotation maps of AGN to look for statistically significant transverse gradients. Analysis of transverse profiles of AGN jets The presence of helical B fields can also give rise to charac-teristic transverse polarization structures; fitting models can give estimates for the pitch angle and viewing angle of the helical field. Gabuzda, Cantwell & Cawthorne 2013 Murphy, Cawthorne & Gabuzda 2013

  13. 5-credit projects (PY4114) Calculating the polarization and Faraday rotation of AGN cores using a simple model The core regions of AGN sometimes show clear Faraday rotation gradients – but are these optical depth effects? Composing a database of AGN images and posting them on the web The UCC AGN group has obtained data for a sample of AGN at 18, 20, 21 and 22cm. The calibration is done, but images need to be made and put on our website.

  14. Unpolarized (tangled) cats.

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