Transcript Document

Radio Galaxies
part 4
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 > 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).
Example of broad line radio galaxy (3C390.3)
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
 Ionization parameter:
ratio between ionizing photon flux/gas density
 Temperature of the emitting gas
 Mass of the emitting gas
photoionization
models for different
ionization parameters
Examples of
diagnostic diagrams
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
Powerful radio galaxies: energetics
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Radiation
Quasar luminosity:1044 — 1047 erg s-1
Luminosity integrated over lifetime:1057—1062 erg
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Jets
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Winds Total wind power:1043 — 1046 erg s-1
Jet power:1043 —1047 erg s-1
Jet power integrated over lifetime: 1057 — 1062 erg
Wind power integrated over lifetime:1056 — 1061 erg
+ Starburst-induced superwinds….
Emission line nebulae: what can we learn?
Emission line haloes: <1kpc scale
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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 nearnuclear regions
the presence of the nuclear activity could influence the evolution
of the galaxy (e.g. clear gas away from the nuclear regions)
Cygnus A
viewed by
HST
NICMOS 2.0mm
Optical images
2.0 micron image
HST/NICMOS
Evidence for a super-massive black hole in Cygnus A
Correlation between black hole mass and
galaxy bulge mass/luminosity
Cygnus A
 broad permitted line seen in
polarized line: only the scattered
component can be seen
Broad- and narrow line radio galaxies
become undistinguishable
Emission line nebulae: 1-5kpc scale
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Kinematics.
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Ionization.
Emission line kinematics a
combination of AGN-induced and gravitational
motions
the AGN
Outflows.
Gas predominantly photoionized by
Clear evidence for emission line
outflows in Cygnus A and some compact radio
sources, but outflow driving mechanism uncertain
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
Emission lines in (powerful) radio galaxies
6
[O III]λλ4959,5007
z = 0.1501 ± 0.0002
FWHM ~ 1350 km s-1
Relative flux
4
2
Δz ~ 600 km s1
[O II] λλ3727
[O III]
z = 0.1526 ± 0.0002
FWHM ~[O650
s-1
II] km
[Ne III]
H
[Ne V]
Wavelength (Å)
(Tadhunter et al 2001)
Diagnostic diagrams including ionization from shocks
Emission line nebulae: 5-100kpc scale
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Kinematics.Activity-induced gas motions are important
along the full spatial extent of the radio structures,
regardless of the ionization mechanism
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Jet-induced shocks.
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Gravitational motions.
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Starbursts.
The shocks that boost the
surface brightness of the structures along the radio axes also
induce extreme kinematics disturbance
Require full spatial mapping of
the emission line kinematics in order to disentangle
gravitational from AGN-induced gas motions
Starburst-induced superwinds may also
affect the gas kinematics out to 10’s of kpc
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.
Emission line “clouds” in the halo of CenA
CenA: D~3Mpc
Mgas  mp
L(H )
ne Heff hH
hH energy of an H photon (erg )
ne electron density (cm 3 )
mp mass of the proton (kg )
L(H  ) lu minosity of H  line (erg s 1 )
 Heff effectiverecombination coefficient for H  (cm 3 s 1 )
1000 km/s
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
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?
Any difference (in the optical lines) between
low and high power radio galaxies?
What makes the difference?
Well known dichotomy:
low vs high power radio galaxies
Differences not only in the radio
WHY?
high-power
radio galaxy
Intrinsic differences in the
nuclear regions?
Accretion occurring at low
rate and/or radiative efficiency?
No thick tori?
low-power
radio galaxy
The central regions of low-power radio galaxies
No optical core
Optical core
No strong obscuration: optical core very often detected
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 haven’t seen broad permitted lines
More on the host galaxy
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
3C305
3C293
Results from
UV imaging
3C321
Allen et al.
2002
The young stellar component may come from
a recent merger
o We can use the age of the stars to date when this merger
occurred
o To be compared with the age of the radio source