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