From Cooling-Flows to Cool Cores CLUSTERS OF GALAXIES

From Cooling-Flows From Cooling-Flows to Cool Coresto Cool Cores

CLUSTERS OF GALAXIES

ForwardForward

About 7 years ago 2 new X-ray About 7 years ago 2 new X-ray satellites have been launchedsatellites have been launched

X-ray Observatories

After the rocket experiments during the 1960s, the first X-ray Earth-orbiting explorers were launched in the 1970s:

Uhuru, SAS 3, Ariel5 followed in late 1970s early 1980s

by larger missions: HEAO-1, Einstein, EXOSAT, and Ginga.

X-ray Observatories

In the 1990s the ROSAT survey detected more than 100,000 X-ray objects

the ASCA mission made the first sensitive measurements of the X-ray spectra from these objects

BEPPOSAX contributed along this line

Current X-Ray Missions

XMM-Newton

Chandra

The X-ray Telescope Chandra

Chandra detectors

PSF

DISPERSIVE SPECTROMETERSDISPERSIVE SPECTROMETERS

All convert into dispersion angle and hence into focal plane position in an X-ray imaging detector•BRAGG CRYSTAL SECTROMETERS (EINSTEIN, SPECTRUM X-GAMMA): Resolving power up to 2700 but disadvantages of multiplicity of cristals, low throughput, no spatially resolved spectroscopy n x = 2d x sin •TRANSMISSION GRATINGS (EINSTEIN, EXOSAT, CHANDRA) m x = p x sin where m is the order of diffraction and p the grating period•REFLECTION GRATINGS (XMM) m x = p (cos - cos)The resolving power for gratings is given by , assuming a focal lenght f and a position X relative to the optical axis in the focal plane X = f tan f sin X = f so is constant

mp

RXX

1

Previous X-ray telescopes had either good spatial resolution or spectral resolution

Rosat Good Spatial resolutionLow or no Spectral resolution

ASCALow Spatial resolutionGood Spectral resolution

Chandra got both

ChandraChandra Versus Previous Generation Versus Previous Generation X-ray SatellitesX-ray Satellites

ASCA view of “the creation” ofMichelangelo

Rosat view of “the creation” ofMichelangelo

Chandra Versus Previous Generation X-ray Satellites

An Imaginary TestChandra view of “the Creation”

of Michelangelo

The RGS ResultThe RGS ResultA1795 Tamura et al. A1795 Tamura et al.

(2001a); A1835 Peterson et (2001a); A1835 Peterson et al. (2001); al. (2001);

AS1101 Kaastra et al. AS1101 Kaastra et al. (2001); A496 Tamura et al. (2001); A496 Tamura et al.

(2001b); sample of 14 (2001b); sample of 14 objects Peterson et al. objects Peterson et al.

(2003)(2003)There is a remarkable lack of emission lines

expected from gas cooling below 1-2 keV.

The most straightforward

interpretation is that gas is cooling down to

2-3 keV but not further.Peterson et al. (2001)Peterson et al. (2001)

Standard CF model predicts gas with T down to at least 0.1 keV!

The EPIC ResultThe EPIC Result

EPIC has a spectral resolution ~ 10 EPIC has a spectral resolution ~ 10 times worse than RGS.times worse than RGS.

It cannot resolve individual lines. It cannot resolve individual lines.

However it can discriminate btwn. However it can discriminate btwn. models with and without a minimum models with and without a minimum temperaturetemperature

The major discriminant is the Fe L The major discriminant is the Fe L Shell blend profileShell blend profile

Comparison btwn. multi-Comparison btwn. multi-temperature modelstemperature models

Spectra above ~1.3 keV are similar.

Below we observe a prominent line-like

feature: Fe-L shell line complex.

In the spectrum with Tmin=0.1 keV we see a

shoulder down to ~ 0.8, this is due to low

ionization lines from gas colder than 0.9 keV.In the spectrum with

Tmin=0.9 keV the shoulder is absent because the

low ionization lines are missing

Molendi & Pizzolato (2001)

Tmin=0.9 keV

Tmin=0.1 keV

Model spectra degraded to the EPIC resolution

EPIC vs. RGS TEPIC vs. RGS Tminmin

EPIC minimum temperatures are in good agreement with RGS minimum temperatures.The result on Tmin is a solid one!

All clusters observed so far show a

Tmin

Values range between ~1 and ~3 keV

An attempt to save CF models (Fabian An attempt to save CF models (Fabian et al. 2001)et al. 2001)

How can we have gas cooling below ~1 How can we have gas cooling below ~1 keV keV

without observing low ionization lines?without observing low ionization lines?

Way out: hiding the flow

Way out: Hiding the flow

Gas MixingFor r< 20 kpc gas with T~103 K is present. Mixing of hot, T ~3•107 K with cold gas may rapidly cool the hot gas to T ~ 3 • 105 K

Gas at temperatures of T~103 K is seen in the innermost ~ 20-30 kpc of only some clusters, thus it may only work for the inner regions of some objects.


Differential Absorption

The absorber could be patchy and concentrated near the center and perhapes absorb the gas producing the lines which are not seen.

A few of the clusters observed so far have at their center an AGN visible at X-ray wavelengths. The spectra of these AGN do not show any evidence of absorption.


Bi-modal metallicity (very ingenuous!)If metal distribution is highly bimodal (e.g. 10% of gas with Z=3 and 90% of gas with Z=0), with Z rich gas in small clumps (r < 1 kpc), for T> 2 keV Z rich and poor

gas would cool togheter, for T< 2 keV, when line emission becomes an important coolant, Z rich gas

would cool much more rapidly than Z poor gas

Observed spectra are not well fit with bi-modal spectral models.

ConsequencConsequenceses

MultiphasenessMultiphaseness Gas is NOT multiphase, at least Gas is NOT multiphase, at least not in the sense required by the not in the sense required by the standard multi-phase CF modelstandard multi-phase CF model

Multiphaseness is or was a Multiphaseness is or was a fundamental ingredient of the CF fundamental ingredient of the CF model, without it the model falls!model, without it the model falls!

Intrinsic AbsorptionIntrinsic Absorption

•Cooling flow spectrum characterized by intense soft Cooling flow spectrum characterized by intense soft emissionemission

•Spectrum with TSpectrum with Tminmin~ 1 keV not as much~ 1 keV not as much

•If you want to reproduce a spectrum with a TIf you want to reproduce a spectrum with a Tminmin~ 1 ~ 1 keV keV with a CF model you have to get rid of the soft with a CF model you have to get rid of the soft emissionemission

•A possible way is to assume intrinsic absorptionA possible way is to assume intrinsic absorption

•The large absorption column depths inferred by The large absorption column depths inferred by previous previous analysis are an artifact resulting from the application analysis are an artifact resulting from the application of anof an incorrect model to the data incorrect model to the data

•Little evidence of gas cooler than 1-2 keVLittle evidence of gas cooler than 1-2 keV anywhereanywhere

•If gas does not cool below 1-2 keV it will not If gas does not cool below 1-2 keV it will not bebe deposited as cold gasdeposited as cold gas

•The gas could still be multi-phase on scales The gas could still be multi-phase on scales we do we do not resolve with XMM/EPICnot resolve with XMM/EPIC

•However at least in the case of M87 our However at least in the case of M87 our resolution resolution is of a few kpc is of a few kpc

Mass DepositionMass Deposition

RGS detects only very weak lines from gas RGS detects only very weak lines from gas cooler than ~ 1 keV (Peterson et al. 2003)cooler than ~ 1 keV (Peterson et al. 2003)

occurs on scales which are not spatially occurs on scales which are not spatially resolvedresolvedby EPICby EPIC

Mass DepositionMass Deposition

Mass deposition is smaller and confined to smaller scales than

previously thought

The old problem of not finding The old problem of not finding abundant cooled gas is solvedabundant cooled gas is solved

Now that we have brought the house down it is time to think about rebuilding

Let’s try with a fresh point of view, let us go to Chandra observation.

Chandra has a very sharp eye, PSF better than 1 arcsec about 10 times

better than XMM-Newton EPIC

The Chandra View

Chandra finds what appear to be holes

“cavities”.Radio lobes are

conicident with X-ray cavities

Radio lobes inflated by jets appear to be

making their way pushing aside the X-ray emitting plasma

Hydra A

McNamara et al. (2001)

The Chandra ViewThe Chandra ViewAbell 2052 Blanton et al. (2001)

Radio lobes fill X-ray cavities Radio lobes fill X-ray cavities Cavities are surrounded by denser & cooler gasCavities are surrounded by denser & cooler gas

The Chandra ViewThe Chandra ViewCentaurus, Sanders et al. (2001), Taylor et al. (2001)

Radio X-ray interaction produces an unusual Radio X-ray interaction produces an unusual radio source with small bent lobesradio source with small bent lobes

The Chandra ViewThe Chandra ViewPerseus, Fabian et al. (2000)

Radio lobes fill X-ray cavities. Inner cavities surrounded by denser & Radio lobes fill X-ray cavities. Inner cavities surrounded by denser & cooler gas. Holes appear to be devoid of ICM, Schmidt et al. (2002) cooler gas. Holes appear to be devoid of ICM, Schmidt et al. (2002)

If we assume that the radio lobes are in pressure equilibrium with the If we assume that the radio lobes are in pressure equilibrium with the surrounding ICM, this is reasonable as no shocks are observed, then surrounding ICM, this is reasonable as no shocks are observed, then

it is easy to show that the lobes filled with B field and relativistc it is easy to show that the lobes filled with B field and relativistc particles have a smaller specific weight than surrounding ICM and particles have a smaller specific weight than surrounding ICM and

should therefore detach and rise buoyantlyshould therefore detach and rise buoyantly. .

The Chandra ViewThe Chandra ViewAbell 2597, McNamara et al. (2001)

Cavities in Abell 2597Cavities in Abell 2597 are not coincident withare not coincident with bright radio lobes. bright radio lobes. Instead, they are associated withInstead, they are associated with faint extended radio emissionfaint extended radio emission seen seen

in a deepin a deep Very Large Array radioVery Large Array radio map. Ghost cavities are likely map. Ghost cavities are likely buoyantlybuoyantly rising relics of arising relics of a radio outburst that occurredradio outburst that occurred between 50 between 50

and 100and 100 Myr ago.Myr ago.

Expanded view of the central region of Abell 2597 after subtracting a smooth background cluster model. The 8.44 GHz radio contours are superposed

VLA 1.4 GHz image of Abell 2597 at 11’’×6’’ resolution

The core of CF clusters is far from being The core of CF clusters is far from being relaxed, interaction with AGN is clearly relaxed, interaction with AGN is clearly present.present.Radio Jets open up as radio lobes plowing Radio Jets open up as radio lobes plowing their way through the ICM.their way through the ICM.Radio lobes are in pressure equilibrium Radio lobes are in pressure equilibrium with ICM, no strong shocks observed.with ICM, no strong shocks observed.Bubbles of low density plasma rise Bubbles of low density plasma rise through cluster atmosphere. Rising speed through cluster atmosphere. Rising speed ~ a fraction of v~ a fraction of vss, rise timescales of the , rise timescales of the order of 10order of 108 8 yrs, ~ to cooling timescale yrs, ~ to cooling timescale

Higher density gas at rims, either Higher density gas at rims, either dragged out from center or compressed dragged out from center or compressed by uprising bubblesby uprising bubbles

The overall pictureThe overall picture

Heating the Heating the flowflow

Feedback from AGN may provide a Feedback from AGN may provide a valid heating mechanismvalid heating mechanism

1.1.Mixing of relativistic plasma with Mixing of relativistic plasma with ICMICM

2.2.Adiabatic expansion of bubbles as Adiabatic expansion of bubbles as they rise through cluster they rise through cluster atmosphereatmosphere

3.3.Dragging out of dense gas from core Dragging out of dense gas from core which expands adiabatically which expands adiabatically becomes less dense and eventually becomes less dense and eventually mixes with ambient gasmixes with ambient gas


Feedback from AGNFeedback from AGN

• Gas cools everywhere in the core, Gas cools everywhere in the core, cavities are not seen everywhere cavities are not seen everywhere

• Some cores do not host an active Some cores do not host an active radio source (e.g. A2597) radio source (e.g. A2597)

A possible solution is to assume a A possible solution is to assume a duty cycle, note that the timescale duty cycle, note that the timescale over which radio lobes evolve must over which radio lobes evolve must be ~ a few times shorter than the be ~ a few times shorter than the cooling time scale. cooling time scale.

The energetic requirements, at least The energetic requirements, at least in some cases could be met. in some cases could be met.


Feedback from AGNFeedback from AGN

Fabian et al. (2002)

The total energy required to quench a flow can be

consider-able.

Take total cooling energy, determined from L(<

rcool )•tHubble for a set of clusters and compare it with the total energy emitted by

an AGN over tHubble.

The more luminous cores imply very large black-hole

masses


ConductionConduction

Large heat reservoir in outer regions of clusterLarge heat reservoir in outer regions of cluster

Conduction and B Field. If the B field isConduction and B Field. If the B field is chaotic over chaotic over a widea wide range of length scalesrange of length scales as might happen as might happen

with MHD turbulence conductivity can be as high with MHD turbulence conductivity can be as high as 1/3 Spitzer (Narayan & Medvedev 2001).as 1/3 Spitzer (Narayan & Medvedev 2001).

Large ΔT/T in cores => conduction should be Large ΔT/T in cores => conduction should be efficentefficent


ConductionConduction

Effective Effective conduction conduction

drdTrrL

eff /)(

24

Fabian et al. (2002)

Most clusters have κeff between

κs and 1/10κs

Conduction is potentially important


ConductionConductionFrom 3d structure From 3d structure

it is possible to it is possible to derive estimate of derive estimate of

κκeffeff(r)(r)

Ghizzardi et al. (2003), Voigt et al. (2002)

For outer regions κeff is between κs

and 1/3κs , for innermost regions

κeff exceeds κs.

Conduction cannot quench CF in the very center


Mixed modelsMixed models

Some authors have considered “mixed” Some authors have considered “mixed” modelsmodels

Heating from conduction in outerpartsHeating from conduction in outerpartsHeating from AGN within 20-30 kpcHeating from AGN within 20-30 kpc

SummarySummary

The old revered Cooling-Flow model has fallen The old revered Cooling-Flow model has fallen under the weight of new observations obtained under the weight of new observations obtained

mainly with XMM-Newton.mainly with XMM-Newton. Chandra images show that the cores of Chandra images show that the cores of

clusters far from being relaxed, are the sight of clusters far from being relaxed, are the sight of much dynamical activity. much dynamical activity.

Interaction between radio lobes and ICMInteraction between radio lobes and ICM

Current efforts are concentrated on finding Current efforts are concentrated on finding plausible heating sources to balance the CF plausible heating sources to balance the CF AGN play a role in the innermost 20-30 kpcAGN play a role in the innermost 20-30 kpc

and conduction may operate at larger radii and conduction may operate at larger radii

Documents

From Cooling-Flows to Cool Cores CLUSTERS OF GALAXIES