Radio Galaxies part 4

copygrouperMechanics

Nov 13, 2013 (3 years and 8 months ago)

146 views

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

Examples of

diagnostic diagrams

photoionization

models for different

ionization parameters

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 10
8
cm
-
3

(from the absence of broad forbidden lines)



typical velocities 3000
-
10000 km/s

Narrow line regions (NLR):



typical density 10
3

to 10
6
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
:
10
43



10
46

erg s
-
1

Wind power integrated over lifetime
:
10
56



10
61

erg

Jet power
:
10
43

10
47

erg s
-
1

Jet power integrated over lifetime
:

10
57



10
62

erg

Quasar luminosity
:
10
44



10
47

erg s
-
1

Luminosity integrated over lifetime
:
10
57

10
62

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 2.0
m
m

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

"
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 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

Relative flux

2

4

6

[O III]
λλ4959,5007

z =
0.1501
±

0.0002

FWHM ~ 1350 km s
-
1

[O II]

[Ne III]

[O III]

H


[Ne V]

[O II]
λλ3727

z =
0.1526
±

0.0002

FWHM ~ 650 km s
-
1

Δ
z ~ 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
)
(
)
(
)
(
)
(
)
(
1
3
1
3




s
cm
H
for
t
coefficien
ion
recombinat
effective
s
erg
line
H
of
osity
lu
H
L
kg
proton
the
of
mass
m
cm
density
electron
n
erg
photon
H
an
of
energy
h
h
n
H
L
m
M
eff
H
p
e
H
H
eff
H
e
p
gas













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 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?

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
-
power

radio galaxy

high
-
power

radio 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 from

UV 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