Radiogalaxies and jetted AGN: discovery, properties and impact

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Radio-galaxies and jetted AGNdiscovery,
properties and impact

• Historical perspectives
• The family of radio-loud AGN
• The unified model of radio-loud AGN
• FRI and FRII radio galaxies
• Jets
• Formation and basic properties
• Superluminal motion
• Jets and the cooling flow problem

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IV.10 The discovery of AGN

• Early 1960s
• Radio astronomers started to survey the sky
• Found many mysterious radio sources
• Quasi-stellar radio sources (quasars for short)
• Very difficult to identify radio images were too
  fuzzy to allow quasars to be localized on sky
• Cyril Hazard
• Used Lunar occultation to localize 3C273
• I.e., measure the precise time when the radio
  signal from the quasar is blocked by the Moon
• then use knowledge of the Moons position to
  determine position of quasar.
• Hazard could localize 3C273 to about 1 arcsec.

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Parkes
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• M.Schmidt
• Took Hazards position and observed it with
  optical telescope in particular, he took a
  spectrum
• Clearly observed emission lines of hydrogen, but
  spectrum showed huge redshift, z0.158
• Hubbles law ? huge distance (747 Mpc using WMAP
  cosmology)
• Thus, object must be 1000x more powerful than
  regular galaxy

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IV.11 Radio-loud AGN

• 3C273 is an example of a radio-loud AGN a
  significant fraction of its luminosity emerges in
  the radio band
• Nature of radio-loud AGN
• Detailed studies with radio interferometers
  showed that radio emission was often coming from
  an extended region
• Often showed a double structure
• Martin Rees suggested that the radio emission is
  powered by jets emerging from the immediate
  region around a black hole

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Cygnus-A
Cygnus-A
FRII high power systems that brighten at the
edges (edge-brightened). Often look like
directed explosions.
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Of course, jets arent only seen in the radio
band!
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The zoo of radio-loud AGN

• Radio-galaxies
• Strong extended radio emission but rather weak
  nucleus display either narrow optical emission
  lines (NLRG) or broad optical emission lines
  (BLRG)
• Radio-loud quasars
• Strong extended radio emission and a
  strong/variable nucleus showing broad optical
  emission lines
• Blazars
• Strong and variable emission across the whole
  spectrum no emission lines highly polarized

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Unified model of AGN difference between
radio-loud quasars and radio-galaxies is
orientation
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Radio-galaxies are sub-divided into
Faranoff-Riley (FR) classes
FR-I low power systems that are bright in the
center and then fade off at the edges, i.e.,
edge darkened. Look like smoke-stacks
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Cygnus-A
Cygnus-A
FRII high power systems that brighten at the
edges (edge-brightened). Often look like
directed explosions.
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Whats wrong with this galaxy?
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IV.12 Properties of jets

• We want to know
• How fast are jets traveling?
• How much energy do they carry?
• What are they made of?
• Normal matter (protonselectrons)?
• Pair plasma (electronspositrons)?
• Poynting flux?
• How are they accelerated and collimated?
• Why do some AGN have jets and others do not?

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IV.12 Properties of jets

• We want to know
• How fast are jets traveling?
• How much energy do they carry?
• What are they made of?
• Normal matter (protonselectrons)?
• Pair plasma (electronspositrons)?
• Poynting flux?
• How are they accelerated and collimated?
• Why do some AGN have jets and others do not?

?
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How fast are jets traveling?

• Best constraints come from direct observations of
  blobs moving in AGN jets
• In some jets, see superluminal motion apparent
  motion exceeding the speed of light
• Strong evidence that the jet material is moving
  at relativistic velocities see discussion on
  board

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How much energy is carried by jets?

• Generally hard to determine
• Can estimate power if we see interaction of jet
  with surroundings
• E.g., jets can blow bubbles in the hot (X-ray
  emitting) gas
• Can estimate power needed to blow bubbles

Central galaxy of the Centaurus cluster
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How are the jets powered?

• Dont know how jets are powered! But we know
  that some jet sources are efficient
• Use X-ray observations to estimate density
  temperature of hot gas close to BH
• Then compute Bondi accretion rate find efficient
  conversion of accreted mass-energy into jet power
• Probably has something to do with winding of
  B-fields by the accretion disk

Allen et al. (2006)
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IV.13 The heating of the ISM/ICM by AGN jets

• Back to the effect that AGN jets have on massive
  galaxies and cluster cooling flows
• Computer simulations can be used to model the
  interaction of jets with the surrounding ISC/ICM

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3-d single-burst case / Density (ZEUS-MP v1.5)
Pure cooling
Single-burst jet
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Instantaneous fueling scenario
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Instantaneous fueling scenario
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Delayed fueling scenario
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Delayed fueling scenario with ICM rotation
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Unsharp mask of the 900ks Chandra observation of
the Perseus cluster (Fabian et al. 2005)