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Jets from Active Galactic Nuclei: Observations and Models

Jets from Active Galactic Nuclei: Observations and Models. S. Massaglia DFG: A. Ferrari, T. Matsakos, O. Tesileanu, P. Tzferakos INAF-OATo: G. Bodo, A. Mignone, P. Rossi, E. Trussoni Enrico Fermi Institute, University of Chicago Department of Astronomy, University of Athens

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Jets from Active Galactic Nuclei: Observations and Models

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  1. Jets from Active Galactic Nuclei:Observations and Models S. Massaglia DFG: A. Ferrari, T. Matsakos, O. Tesileanu, P. Tzferakos INAF-OATo: G. Bodo, A. Mignone, P. Rossi, E. Trussoni Enrico Fermi Institute, University of Chicago Department of Astronomy, University of Athens Marie Curie project JETSET Congresso DFG, Aprile 2008

  2. Overview • Normal and Active Galaxies • Jets from Radio Galaxies • Modelling Jets by Numerical Simulations: comparison with observations • Conclusions

  3. Normal Galaxies Stars contribute to the radiation emission, limited to the optical band and whereabouts. Typically, 1011 stars of a galaxy emit a luminosity of about 1044 ergs s-1 (1011 L)

  4. Active Galaxies Few galaxies ( percent) are “pathological”: The main contribution to the luminosity is not from stars but from an Active Nucleus R  30 kpc L  2 kpc L  10-5 kpc

  5. Active Galaxies 2. The emission is not confined to the optical band but extends to other frequencies.

  6. Motivations Why studying Active Galaxies: For investigating the formation and merging events during the life of galaxies. 2. To understand the formation of cluster of galaxies. 3. Active Galactic Nuclei are a likely source of the most energetic cosmic rays.

  7. Radio Galaxies and Jets The most prominent feature in some active galaxies are collimated outflows of matter in form of radio jets. These galaxies are then called radio galaxies. 3C 31 3C 98

  8. Radio Galaxies Synchrotron Radio to X-rays Radio emission Synchrotron: F()  -   0.5 Electron power law distribution n(E)  E-p p=2+1 Pictor A (z=0.035) Nucleus to hot-spot  270 kpc jet  120 kpc Radio: synchrotron X-rays: synchrotron+IC

  9. Very Large Array 27 radio antennas in a Y-shaped configuration on the Plains of San Agustin fifty miles west of Socorro (NM). Each antenna is 25 m in diameter. The data from the antennas is combined electronically to give the resolution of an antenna 36 km across, with the sensitivity of a dish 130 m in diameter

  10. Origin of Radio Jets from AGNs: The Black-Hole Paradigm Jets originate around SMBH of 108-1010 M accreting mass through a magnetized disk

  11. Are Active Galaxies peculiar objects or a phase of their life common to most of them? At the centers of many normal galaxies the presence of a SMBH has been detected by indirect means. At the center of the Milky Way there is a BH of one million solar masses

  12. Radio Galaxies: Main facts • Radio luminosity: 1041-1044 ergs s-1 • Size: a few kpc – some Mpc • Life timescale: 107-108 ys • Magnetic fields: 10 – 103G • Kinetic power: 1044-1047 ergs s-1

  13. Modelling Radio Jets Hypothesis: Physics described by the Ideal Magneto-Hydrodynamic Equations

  14. Modelling Radio Jets Relativistic estension of the MHD equations:

  15. Modelling Radio Jets MHD equations can be solved by numerical means only: Define the integration domain and the system of coordinates Set the initial and boundary conditions Set parameters, carry out numerical integration Analyze the results and compare to observations

  16. Basic physical parameters Theoretical modeling andnumerical simulations of jets on large scale require a minimum set of parameters: • Lorentz factor (Γ) • Jet Mach number (M) • Jet-ambient density ratio (η)

  17. Lorentz factor: jet one-sidedness

  18. Jet Mach number: indication of shocks Beq=4.610-4 G

  19. Jet Mach number: indication of shocks

  20. Model of Jet Termination Terminal shock jet

  21. Cygnus A (FR II) - VLA, 6cm

  22. undisturbed intergalactic gas “cocoon” (shocked jet gas) splash point backflow bow shock Cygnus A (FR II) - VLA, 6cm

  23. Numerical simulation Supersonic and Underdense jet We use the (M)HD code PLUTO, based on high resolution shock-capturing schemes. (http://plutocode.to.astro.it Mignone et al. 2007)

  24. Numerical simulation bow-shock Contact discontinuity backflow Mach disk intergalactic gas

  25. Numerical simulations Comparison of observed and simulated morphologies • Relativistic (one-sidedness), Γ>1 • Supersonic (presence hot-spots), M>1 • Underdense (presence of cocoons), η<1 • (simulations) intergalactic gas bow-shock backflow cocoon splash point

  26. Chandra X-ray Observatory Cygnus A Wilson et al. (2001) CXC

  27. Conclusions • The study of the Active Galaxies has a crucial role in astrophysics and cosmic ray physics. • It provides a test ground for new domains of the physics. • Numerical simulations important for the comparison with observations.

  28. Jet instability and braking Jet instabilities: linear growthτKH ~ 2π MJ RJ / cs Nonlinear growth:τKH  10RJ / cs Mixing and mass entrainment Jet braking

  29. Jet instability and braking Rossi et al. 2008)

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