Observational Evidence of AGN Feedback

Author: A.C Fabian

reporter: Jun Xu

Outline

Introduction

The Radiative or Wind Mode

The Kinetic Mode

Summary

Future study

ABCs of AGN Feedback

Radiation, winds and jets from AGN interact with ICM or ISM

May terminate star formation in the galaxy and stifle accretion onto the black hole

This powerful object may strongly impact on their surrounding area in two different mode — Radiative or Wind Mode and the Kinetic mode

Why is AGN feedback important

The binding energy of the galaxy bulge, which is of mass Mgal, is

Egal ≈Mgalσ 2

The mass of the black hole is typically observed to be

MBH=1.4×10-3 Mgal

And assuming a radiative efficiency for the accretion process of

10%

EBH/Egal ≈ 1.4×10-4(c/σ )2

Most galaxies have σ < 400 Km S-1

So EBH/Egal > 80

The Radiative or Wind mode

Also called quasar mode

When AGN is very luminous, accreting close to the

Eddington rate

Most concerned with pushing cold gas about

Strong radiation

Energy: heating Momentum: pushing

MBH − σ relation

For a quasar at the Eddington

limit

based on Energy gives

based on Momentum balance

gives€

MBH ~fσ 5σ T

4πG2mpc

€

MBH =fσ 4σ TπG2mp

Gultekin et al 2009

Radiation pressure on dust

The quasar is locally at Eddington limit, it must far below

the Eddington limit when the moss of the galaxy is

included

Dust embedded in the gas is expected

Ledd is reduced by a factor of σd/ σT, Which is about 1000

for a typical quasar, dropping to 500 for low Eddington

ratio objects

Is this just a coincidence or underlying reason why

Mgal/MBH ∼1000 ?

Radiation pressure on dust

If the repeated action of radiation pressure on dust is

responsible for MBH − σ relation, then

For a constant mass-to-light ration,this corresponds to the

Faber-Jackson(1976) relation

Since Mgal = 2σ2r/G, then

€

Mgal ~fσ 4σ dπG2mp

€

σ 2

r~

2πGmp

fσ d

AGN windsThe main interaction may due to winds, not to radiation pressure.

€

LwLEdd

=f

2

r

rg

v

c ⎛ ⎝

⎞ ⎠

3N

NT

• To produce MBH ∝ σ4 , Lw needs to be proportional to the

Eddington limit, which is plausible if wind is accelerated by

radiation pressure

• The commonest way to observe AGN winds is by line ab-

sorption

of the quasar continuum by intervening wind material

AGN winds•The X-ray warm absorbers commonly seen in Seyfert galax-

ies

flowing at ~1000 km s-1 are insufficient

•Faster winds are required, such as those seen in UV observa-

tion of BAL quasars and X-ray of some AGN with velocities of

tens of

thousands of km s-1 some AGN

•Tombesi et al (2012) estimated mass outflow rate exceeds

5% of the mass accretion rate,and have Lw range from 1042.6 –

1044.6

Galaxy outflows

•Evident of AGN feedback is clearly seen in some galactic

outflows

•Most of the lower velocity winds are considered to be pow-

ered by

stellar processes such as supernova

• Identifying the effects of AGN feedback in outflows relies

on

observing higher velocity (e.g.> 500 km s-1)

•High fuelling rate leads to high obscuration ,makes observa-

tion

more difficult

•Many recent reports of outflows hosting AGN. A spectacular

example is the 1300 km s-1 outflow in a redshift 6.4

quasar(Maiolino et al 2012)

Downsizing problem

• The most luminous and massive AGN peak at earlier

cosmic

times

• Surprising anti-hierarchical behavior in CDM universe

• Something is quenching quasar

The Kinetic Mode

•Also called radio mode

• Which uses the mechanical energy of radio-emitting

•Weak radiation

•Typical operates when the galaxy has a hot halo and the ac-

creting

black hole has powerful jets

Cooling flow problem

•The massive galaxies at centres of groups and clusters are

often

surrounded by gas with a radiative cooling time short enough

that a

cooling flow should be taking place(Fabian 1994)

•A1835 has a star formation rate in a low redshift BCG ~125

Msun yr-1,

Less than uninhibited mass cooling rate which is ~1000 Msun

yr-1

•XMM-Newton RGS provided crucial information against a

simple

cooling flow mode in that they failed to show the strong lines

expected form FeXVII as the gas cooled below 0.7 keV

•Maybe some thing heating the gas. The likely heat source is

the

AGN at the centre of the cool core

Gas properties of some sample

Cooling flow problem

•The general consensus now is that massive black hole at the

centre of the galaxy is feeding energy back into its surround-

ing at a rate to

balancing the loss of energy through cooling

•The accretion flow onto the black hole generates powerful

jets

which inflate bubbles of relativistic plasma

•A study of the brightest 55 clusters originally show that over

70% of those cluster where the cooling time is less than 3Gyr,

therefore

needing heat. An updating make the bubble fraction is >95%

due to projection effect

Bubbles

•The bubbles or cavities, commonly seen in deep Chandra

images of cool core clusters are blown and powered by jets

from central BH

•The innermost bubbles are usually fairly spherical and are

surrounded by a thick pressure region fronted by a weak

shock

•Thermal energy within that region corresponds to 3.7 times

that of a surrounding region of similar volume to the

bubble(Graham 2008)

•Bubbles rise buoyantly in the surrounding hot atmosphere,

turning

into ghost bubbles as they become undetectable in high fre-

quency

Chandra X-ray images

X-ray image of Perseus cluster

Fabian et al. 2006

Bubbles power versus cooling power

Heating/Cooling balance

•The lack of high star formation rates suggest that cooling

does not

exceed heating by ten percent or so.

•The temperature drops indicates that heating does not gen-

erally exceed cooling by much either.

•This represents a relatively close balance which needs to

continue

Over tens to hundreds of bubbling cycles

•If too much gas starts to cool then the accretion rate should

increase

making the heating rate go up and vice versa

Summary•There is clearly enough energy and momentum produced by

the

AGN to expel the interstellar medium of the host galaxy

•It appears that the radiative or wind mode wad most active

when the

AGN was a young quasar. And the galaxy had a large compo-

nent of

cold molecular gas and nucleus was probably highly ob-

scured.

•The kinetic mode is more easily observed, since it is acting

now in

nearby massive objects. The surrounding gas is hot, highly

ionized.

•Although the gross energetics are roughly understood, the

details are not

•An attractive possibility is that the radiative mode shaped

the overall

Galaxy and BH mass at early times, and the kinetic mode has

since

Maintain the situation where needed.

Further study

•Contributions to understanding AGN feedback can be expected

from

all wavebands

•Advanced instruments and telescopes which are planned for

next few

years will help

•In particular, the JAXA/NASA/ESA X-ray observatory ASTRO-H,

to

be launched in 2014, will offer non-dispersive high spectral

resolution

X-ray spectroscopy on a spatial scale of 1.5 arcmin using a mi-

crocalori-meter

Thanks