Radio Galaxies part 4. Apart from the radio the thin accretion disk around the AGN produces optical,...
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Transcript of Radio Galaxies part 4. Apart from the radio the thin accretion disk around the AGN produces optical,...
Radio Galaxiespart 4
Apart from the radiothe 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
Examples of diagnostic diagrams
photoionizationmodels for different ionization parameters
Broad line regions (BLR): typical size (from variability)of 10-100 light-days (Seyferts) up tofew 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 Radiation
Jets
Winds
+ Starburst-induced superwinds….
Total wind power:1043 — 1046 erg s-1
Wind power integrated over lifetime:1056 — 1061 erg
Jet power:1043 —1047 erg s-1
Jet power integrated over lifetime: 1057 — 1062 erg
Quasar luminosity:1044 — 1047 erg s-1
Luminosity integrated over lifetime:1057—1062 erg
Emission line nebulae: what can we learn?
Emission line haloes: <1kpc 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)
Cygnus A viewed by HST
Optical images
NICMOS 2.0m
2.0 micron imageHST/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
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
Example of complex kinematics
(IC5063)
700 km/s
Complex kinematicsof the ionized gas in coincidence with the radio emission:this suggests interaction between radio plasma and ISM
Emission lines in (powerful) radio galaxiesR
elat
ive
flux
2
4
6
[O III]λλ4959,5007z = 0.1501 ± 0.0002FWHM ~ 1350 km s-1
[O II] [Ne III]
[O III]
H
[Ne V]
[O II] λλ3727z = 0.1526 ± 0.0002FWHM ~ 650 km s-1
Δz ~ 600 km s-1
(Tadhunter et al 2001)Wavelength (Å)
Diagnostic diagrams including ionization from shocks
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 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
)()(min)(
)()(
)(
)(
13
1
3
scmHfortcoefficienionrecombinateffective
serglineHofosityluHL
kgprotontheofmassmcmdensityelectronn
ergphotonHanofenergyh
hnHLmM
effH
p
e
H
HeffHe
pgas
1000 km/s
Diagnostic diagrams important to understand which mechanism is dominant
Contours: radio Colors: ionized gas
In some cases the radio galaxy seems to have a strong effect on the medium around.
Radio galaxies at high redshift
Morphology of the extended emission line regionsdepends 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?
Intrinsic differences in the nuclear regions?
Accretion occurring at low rate and/or radiative
efficiency? No thick tori?
Well known dichotomy: low vs high power radio galaxies
Differences not only in the radio WHY?
low-powerradio galaxy
high-powerradio galaxy
Optical core
No optical core
The central regions of low-power radio galaxies
No strong obscuration: optical core very often detected
From HST and X-ray
The HST observations:
Correlation between fluxes of optical and radio cores
High rate of optical cores detected
But so far we haven’t seen broad permitted lines
More on the host galaxy
The optical continuum of Radio Galaxies
3C321
old stellar pop.young stellar pop.
power law
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).
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
Results fromUV imaging Allen et al.
2002
3C305
3C293 3C321
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