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
Jenam Workshop on JETS
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 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: ergs s-1
Size: a few kpc – some Mpc
Life timescale: ys
Magnetic fields: 10 – 103 G
Kinetic power: 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 and numerical 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. Cygnus A (FR II) - VLA, 6cm undisturbed intergalactic gas splash point
“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. (
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 Mixing and mass entrainment
Jet instabilities: linear growth τKH ~ 2π MJ RJ / cs
Nonlinear growth: τKH  10 RJ / cs
Mixing and mass entrainment
Jet braking

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