Radio Galaxies and the Origin of High Energy Cosmic Rays

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Radio Galaxies and the Origin of High Energy
Cosmic Rays

• Silvano Massaglia
• Università di Torino

Catania - CRIS 2006
Cygnus A (z0.056)
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Overview

• Particle acceleration in the hot-spots
• Radio Galaxies Main facts
• Constraining the physical parameters
• Numerical simulations of jets in radio
• galaxies
• Conclusions

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Possible site of Cosmic Ray acceleration Radio
galaxy hot-spots
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Cosmic Ray Acceleration
Fermi mechanism (diffusive shock acceleration
(e.g. Drury 1983)) Emax k Z e B R ? c K1, ?
1 (optimal acceleration) Emax 1018 Z B?G Rkpc
eV ? 1021 eV Spectral distribution n(E) ? E-?,
? ? 1.5-3
UHECRs from the radio galaxy hot-spots?
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About Radio Galaxies
Synchrotron Radio to X-rays
Radio emission Synchrotron F(?) ? ?-? ? ?
0.5 Electron power law distribution n(E) ?
E-p p2?1
Pictor A (z0.035) Nucleus to hot-spot ? 270
kpc jet ? 120 kpc
Radio synchrotron X-rays synchrotronSSC
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Radio Galaxies Main facts
What we know

• Radio luminosity 1041-1044 ergs s-1
• Size a few kpc some Mpc
• Morphologies
• Polarization degree about 1-30

What we guess (but do not know for sure!)

• Life timescale 107-108 ys
• Magnetic field 10 103 ?G
• Kinetic power 1044-1047 ergs s-1
• Jet Mach number Mgt1
• Jet velocity possibly relativistic
• Jet density 10-5-10-4 cm-3

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Radio Galaxies Main facts
Why these uncertainties in constraining the
basic parameters?
Absence of any line in the radiation spectrum!

• Parameters are constrained by indirect means
• Magnetic field by minimum energy
• condition (equipartition)
• Kinetic power energy requirements
• Jet Mach number indication of shocks
• Jet velocity jet one-sidedness
• Jet density jet numerical modelling

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Observed morphologies The Fanaroff-Riley
classification
FR II or lobe dominated (classical doubles)
FR I or jet dominated
3C 31 VLA

3C 98 VLA
FR II only have Hot-spots!
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• FR I Jet dominated emission, two-sided jets,
• typically in clusters, weak-lined galaxies
• FR II Lobe dominated emission, one-sided
  
• jets, isolated or in poor groups, strong
• emission lines galaxies

Radio vs optical luminosities LR ?
Lopt 1.7 (Owen Ledlow 1994) Environment plays
a role?
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Basic physical parameters
Theoretical modeling and numerical simulations of
FR II jets on large scale require a minimum set
of parameters

• Lorentz factor (G)
• Jet Mach number (M)
• Jet-ambient density ratio (?)

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Velocity jet one-sidedness
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NGC 4261
Core
Gap
Jet and counterjet are both visible and proper
motions detected ß0.460.02, ?633
(Piner et al. 2002)
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Difficulties

• The counterjet is not visible in most cases
• Proper motions observed in few objects only

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Jet Mach number indication of shocks
Pictor A
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Jet Mach number indication of shocks
Beq4.6?10-4 G
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Jet Mach number indication of shocks
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Observations of FR II hot-spots
3C445 at the VLT I-band (0.9 ?m) (Prieto et al.
2003)

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FR II hot-spots
Synchrotron models K, H, J and I bands and
radio flux at 8.4GHz

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Modelling the origin of FR II jets
Jets originate around SMBH of 108-1010
M? accreting mass through a magnetized disk
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Modelling the origin of FR II jets
MHD numerical simulations
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Modelling the jet termination in FR II sources
Bow-shock
Mach disk possible cosmic ray acceleration site
Contact discontinuity

• AGN (FRII) jets are
• supersonic (Mgt1)
• Emission non-thermal
• Comparison of model B with Beq

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Modelling the jet termination in FR II sources

Terminal shock
jet
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Jet density from FRII morphologies
Cygnus A (FR II) - VLA, 6cm
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Jet density from FRII morphologies
undisturbed intergalactic gas
cocoon (shocked jet gas)
splash point
backflow
bow shock
Cygnus A (FR II) - VLA, 6cm
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Numerical simulations of FR II
Supersonic and Underdense jet We use the
(M)HD code PLUTO, based on high resolution
shock-capturing schemes. (http//plutocode.to.as
tro.it)
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Numerical simulations of FR II sources
bow-shock
Contact discontinuity
backflow
Mach disk
intergalactic gas
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Numerical simulations of FR II
Comparison of observed and simulated morphologies

• Relativistic (one-sidedness), Ggt1
• Supersonic (presence hot-spots), Mgt1
• Underdense (presence of cocoons), ?lt1
• (simulations)

intergalactic gas
bow-shock
backflow
cocoon
splash point
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Conclusions

• FR II radio galaxies can be site of
• UHECRs in their terminal hot-spots
• Basic physical parameters are still
• unconstrained. Limits from
• observations of morphologies.
• Numerical simulation may play a role
• in contraining the density.