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.