Radio Galaxies

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Radio Galaxies part 4
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Apart from the radio the thin accretion disk
around the AGN produces optical, UV, X-ray
radiation

• The optical spectrum emitted by the gas depends
  upon the abundances of different elements, local
  ionization, density and temperature.
• Photons with energy gt 13.6 eV are absorbed by
  hydrogen atoms.
• In the process of recombining, line photons are
  emitted and this is
• the origin e.g. of Balmer-line spectra.
• Collision between thermal electrons and ions
  excites the low-energy level
• of the ions, downward transition leads to the
  emission of so-called
• forbidden-line spectrum (possible in low
  density conditions).

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Example of broad line radio galaxy (3C390.3)
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• Optical spectrum, what can we derive
• which lines
• flux/luminosity
• width (kinematics)
• ionization mechanism (line ratios)
• density/temperature of the emitting gas
• morphology of the ionized gas
• (any relation with the radio?)
• continuum and stellar population

using spectra and narrow band images
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• Ionization parameter
• ratio between ionizing photon flux/gas density
• Temperature of the emitting gas
• Mass of the emitting gas

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photoionization models for different ionization
parameters
Examples of diagnostic diagrams
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• Broad line regions (BLR)
• typical size (from variability)
• of 10-100 light-days (Seyferts) up to
• few light-years (few x 0.3 pc, quasars).
• electron density is at least 108 cm-3
• (from the absence of broad forbidden lines)
• typical velocities 3000-10000 km/s

• Narrow line regions (NLR)
• typical density 103 to 106 cm-3
• gas velocity 300 1000 km/s
• large range in size from 100-300 pc to tens of
  kpc

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Powerful radio galaxies energetics

• Radiation
• Jets
• Winds

Quasar luminosity1044 1047 erg s-1 Luminosity
integrated over lifetime10571062 erg
Jet power1043 1047 erg s-1 Jet power integrated
over lifetime 1057 1062 erg
Total wind power1043 1046 erg s-1 Wind power
integrated over lifetime1056 1061 erg
Starburst-induced superwinds.
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Emission line nebulae what can we learn?
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Emission line haloes lt1kpc scale

• Kinematics. The emission line kinematics comprise
  a combination of gravitational motions,
  AGN-induced outflows, and AGN-induced turbulence
• Black hole masses. Now possible to determine
  direct dynamical masses for nearby PRG using
  near-nuclear emission line kinematics
• Feedback. The outflow component provides direct
  evidence for the AGN-induced feedback in the
  near-nuclear regions

the presence of the nuclear activity could
influence the evolution of the galaxy (e.g.
clear gas away from the nuclear regions)
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Cygnus A viewed by HST
NICMOS 2.0mm
Optical images
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2.0 micron image HST/NICMOS
Evidence for a super-massive black hole in Cygnus
A
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Correlation between black hole mass and galaxy
bulge mass/luminosity
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• broad permitted line seen in polarized line
  only the scattered component can be seen

Broad- and narrow line radio galaxies become
undistinguishable
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Emission line nebulae 1-5kpc scale

• Kinematics. Emission line kinematics a
  combination of AGN-induced and gravitational
  motions
• Ionization. Gas predominantly photoionized by the
  AGN
• Outflows. Clear evidence for emission line
  outflows in Cygnus A and some compact radio
  sources, but outflow driving mechanism uncertain

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Example of complex kinematics
(IC5063)
700 km/s
Complex kinematics of the ionized gas in
coincidence with the radio emission this
suggests interaction between radio plasma and ISM
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Emission lines in (powerful) radio galaxies
Wavelength (Å)
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Diagnostic diagrams including ionization from
shocks
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Emission line nebulae 5-100kpc scale

• Kinematics.Activity-induced gas motions are
  important along the full spatial extent of the
  radio structures, regardless of the ionization
  mechanism
• Jet-induced shocks. The shocks that boost the
  surface brightness of the structures along the
  radio axes also induce extreme kinematics
  disturbance
• Gravitational motions. Require full spatial
  mapping of the emission line kinematics in order
  to disentangle gravitational from AGN-induced gas
  motions
• Starbursts. Starburst-induced superwinds may also
  affect the gas kinematics out to 10s of kpc

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Gas with very high ionization at 8 kpc from the
nucleus
Even if the nucleus is obscured by the torus, the
extended emission line regions can tell us about
the UV radiation from the nucleus.
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Emission line clouds in the halo of CenA
CenA D3Mpc
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1000 km/s
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Contours radio Colors ionized gas
In some cases the radio galaxy seems to have a
strong effect on the medium around.
Diagnostic diagrams important to understand which
mechanism is dominant
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Radio galaxies at high redshift

• Morphology of the extended emission line regions
• depends on the size of the radio source
• Alignment between the emission lines and the
  radio axis
• Interaction between radio and medium does this
  also trigger star formation?

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Any difference (in the optical lines) between
low and high power radio galaxies?
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What makes the difference?
Well known dichotomy low vs high power radio
galaxies Differences not only in the radio
WHY?
Intrinsic differences in the nuclear regions?
Accretion occurring at low rate and/or
radiative efficiency? No thick tori?
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The central regions of low-power radio galaxies
No strong obscuration optical core very often
detected
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From HST and X-ray
The HST observations

• High rate of optical cores detected

• Correlation between fluxes of
• optical and radio cores

But so far we havent seen broad permitted lines
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More on the host galaxy
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The optical continuum of Radio Galaxies

Usually the old stellar population is the
dominant - as usual in elliptical galaxies - but
in some cases a young stellar population
component is observed (typical ages between 0.5
and 2 Gyr).
3C321

• consistent with the merger
• hypothesis for the triggering
• of the radio activity.
• but not a single type of merger
• AGN appears late after the
• merger

old stellar pop.
young stellar pop.
power law
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3C305
3C293
3C321
Results from UV imaging
Allen et al. 2002
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• The young stellar component may come from
• a recent merger
• We can use the age of the stars to date when
  this merger
• occurred
• To be compared with the age of the radio source

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Cavities created by the radio emission in the
hot (X-ray) gas
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Emission line nebulae what they can tell us

• AGN Physics. Tests of the unified schemes, jet
  physics, black hole masses
• Host galaxy properties. Mass distributions,
  abundances, gas masses
• Galaxy Evolution. Clues to the assembly of
  massive galaxies at both high and low redshifts
• Feedback. The importance of AGN-induced feedback
  effects in the evolution of the host galaxies