Bremsstrahlung fromCLUSTERS OF GALAXIES

Clusters of Galaxies:a short overview

Clusters of GalaxiesX-ray Band

K108R

MT Totgas

GalaxiesGasDarkMatter

1000x1010 Mo

1014 Mo

1015 Mo

X-Ray ImagingX-Ray ImagingX-rays and optical light show us a different picture X-rays and optical light show us a different picture

X-Ray ImagingX-Ray ImagingX-rays and optical light show us a different picture X-rays and optical light show us a different picture

Structure Formation

Structure Formation

1000 galaxies within 1Mpc

Cluster Gas Density

Observables RelationsT-M

Virial Equilibrium

Kinetic Energy for the gas

Thermodynamic

T-M relation

Status of The IGMAge of Clusters ~ few Gyr; R ~ 1-2 MpcAge of Clusters ~ few Gyr; R ~ 1-2 MpcT T ~ 1-10 keV; Gas highly ionized~ 1-10 keV; Gas highly ionized

Electrons free mean path

Gas may be treated as a fluid

Timescale for Coulomb Collisions

Electrons are in kinetic equilibriumMaxwellian velocity distribution

Timescale for soundwave propagation

Gas is in hydrostatic equilibrium

Intracluster Medium

Hydrostatic equilibrium (spherical symmetry)

We can measure the Cluster mass

Dynamical Properties of the Galaxies

Isothermal Cluster King profile Beta Profile

Emission Processes of Clusters of Galaxies in the X-ray Band

•The IGM is a PlasmaThe IGM is a Plasma•Electrons are accelerated by the ionsElectrons are accelerated by the ions•They emit for BremsstrahlungThey emit for Bremsstrahlung

•Electrons are in kinetic equilibrium (Maxwellian V distr. )•Cluster emission is mainly thermal Bremsstrahlung

Emission Processes of Clusters of Galaxies in the X-ray Band

Beside IGM contains some metals (0.3 Solar)

They produce line emission

X-ray Observations

•Gas densityGas density•Gas TemperatureGas Temperature•Gas chemical compositionGas chemical composition

•If assume hydrostatic If assume hydrostatic equilibriumequilibriumCluster MassCluster Mass

Cooling FlowsCooling Flows Observational evidencesObservational evidences

The homogeneous model: one ρ and T at each radius

Observational evidence against homogeneous gasObservational evidence against homogeneous gas

The inhomogeneous model: Δρ and ΔT at each radius

The role of the magnetic fields in Cooling FlowsThe role of the magnetic fields in Cooling Flows

Estimates of dM/dt from imaging & spectral data

The fate of the cooling gasThe fate of the cooling gas

Cooling in Clusters

LX ngas2 Tg

1/2 Volume

E ngasKTg Volume

tcool E/LX Tg1/2 n-1

Cooling FlowsCooling Flows

tcool ≈ Tg1/2

np-1

For large radii np is small tcool »tHubble

In the core np is large tcool ~ tHubble

The gas within The gas within rrcoolcool will cool will cool

Cooling FlowsCooling Flows

When the gas coolsWhen the gas cools

The pressure becomes lowerThe pressure becomes lower

The gas flows inwards,The gas flows inwards,

The density increases in the The density increases in the centercenter

The gas cools even fasterThe gas cools even faster

Observational Evidences Observational Evidences for Cooling Flowsfor Cooling Flows X-Ray ImagingX-Ray Imaging

Surface brightness strongly peaked at the Surface brightness strongly peaked at the centercenter

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

m

p

RX

X

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 Test

Chandra 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!

AGN in the central galaxy

Chandra X-ray ObservatoryHydra A - X-ray

X Ray Radio

Chandra Observation of A2052; Blanton et al. 2001 ApJ, 558, L15

Interaction between radio sources and X-ray gas

Hydra A; McNamara et al 2000; David et al. 2001Perseus; Fabian et al. 2000Virgo; Young et al. 2002

Chandra Observations of Clusters

A 133Fujita et al. 2002

A 1795Fabian et al 2001

1E0657Markevitch et al 2001

Chandra OBSERVATION OF 2A0335

P. Mazzotta., A. Edge, Markevitch 2002, submitted

The Chandra ViewThe Chandra View

Abell 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

Cluster MergerDensity Entropy

1E0657Markevitch et al 2001.