Kein Folientitel

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Merging galaxy clusters radio and X-ray
studies

• hierarchical structure formation in the
  universe
• still ongoing at z 0
• X-ray substructure
• radio emission
• cluster weather
• cosmological shocks
• weather in cluster gas

themes of a commencing graduate school ...
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Large-scale structure

• clusters are powerful testbeds for cosmological
  models
• - cluster mass and abundance ? ?M 1
• - gravitational lensing ? ?? ? 0.7
• - cluster abundance with z ? ?M 0.25 0.1

• numerical simulations predict large-scale
  structure in the presence of (dominating) CDM,
  with ongoing collapse of the largest structures
  at z 0

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Clusters of galaxies

• groups and clusters of galaxies largest
  gravitationally bound and collapsed systems in
  the universe
• groups 3 ? 30 galaxies
• clusters up to a few 1000
• R 2 Mpc
• M 1014 1015 M ?

• Local Group 35 members
• MW, M31, M33 all others dwarf galaxies

• Virgo Cluster 2100 members (Binggeli et al.
  1985)

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m1

• Abell Catalogue (POSS ESO SSS) 1682
  clusters (Abell 1958) 4073
  (Abell, Corwin Olowin 1989)
• criterion ? 50 galaxies with m3 ? m ? m3
  2
• contained within Abell Radius ?A
  1.5/z, i.e. RA 1.5 ? h-1 Mpc
• covers 0.028 lt z lt 0.20

m2
m3
m32
? 50
cD - single dominant cD galaxy (A2029, A2199)
B - dominant binary, like Coma F - flattened
(IRAS 091044109) L - linear array of galaxies
(Perseus) C - single core of galaxies I -
irregular distribution (Hercules)
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Böhringer (1996)
Structures of galaxy clusters

• 3 mass components visible galaxies, ICM, DM
• - galaxies 3 (optical, IR)
• - ICM 10 15 (X-rays)
• - DM 80 (?v , grav. lensing)

Coma

• belief until mid 80s clusters are simple
  ...
• however ample evidence for substructure,
  rendered visible most convincingly in X-ray
  regime ? true-nature-images
• of clusters!
• radial variations of centroids
• twists in X-ray isophotes (e.g. Coma Cluster!)
• non-Gaussian skewed or even bimodal f(v)s

A578 A1569
A3528
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X-ray morphologies of clusters
Optical techniques barely disclose gravitational
potential in nearby clusters unless these are
rich (too few test particles) distant ones
lensing ...

• X-rays continuous mapping of ? in galaxy
  clusters
• systematic imaging EINSTEIN, ROSAT
• hígh spatial rersolution CHANDRA
• spectral XMM
• mapping of T ASCA

Fornax Cluster
Abell 2256
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• systematic X-ray survey of galaxy clusters
  REFLEX (Böhringer et al. 1999)
• basically 1000s of clusters, mostly with but
  few (? 100) photons...
• 452 clusters, 53 Abell (only!)
• for ?m 0.3 ? cluster mass contributes 6 to
  total matter in the Universe

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Radio emission from clusters of galaxies
Another diagnostic tool of cluster physics
radio emission synchrotron radiation
Clarke et al. (1999)

• is the IGM/ICM magnetizied?
• how (and when) did it get magnetized? AGN
  (standard) dwarf galaxies (Kronberg et al.
  1999)
• evidence for B-fields

- radio halos relics (e.g. Feretti 1999)
Enßlin Biermann (1998)
- Faraday rotation ? ? 5 ?G (Clarke et al.
1999)
- Inverse Compton emission ? ? 1 ?G
(e.g Enßlin Biermann 1998 Tsay et al. 2002)
IC results not yet conclusive
Dixit deus Fiat lux (campus magnetibusque)
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Thierbach et al. (2002)
Feretti Giovannini (1998)

• radio halos central, diffuse, polarization
  lt 5

• radio relics peripheral, ? 20 polarized

• no obvious particle/energy sources
• steep(ening) spectra at higher frequencies
• how frequemt? many if searched for with
  scrutiny!

Röttgering et al. (1999)
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Weather stations in galaxy clusters

• 10 of galaxies in clusters produce significant
  radio synchrotron emission (P? ? 1023 W Hz-1 at
  ?20 cm)
• jets of radio plasma ejected from galaxy cores,
  forming lobes and tails ? probe relative gas
  motions over 100s of kpcs (NATs, WATs)

• former belief tails simply trace ballistic
  motions of galaxies when radio plasma is exposed
  to ICM ram pressure (radius of curvature R , jet
  radius rj , jet velocity vj , galaxy velocity vg
  , density of jet ?j , density of ICM ?ICM
  density of ICM)

• however 90 of WATs NATs in clusters with
  X-ray
• substructure correlation between elongations in
  X-rays and bending of radio tails
• cluster mergers ? bulk flow ? ram pressure ?
  bends of radio tails and distortion of X-ray
  surface brightness
• Perseus Cluster (Sijbring 1994) low-frequency
  kinks and bends suggest highly non-ballistic
  motions ? caused by turbulent motions of the ICM
  plasma! ? high winds
• synchrotron ages from break frequency ?b (GHz),
  equipartition magnetic field Beq (?G), equivalent
  magnetic field of CMB BCMB (?G)

3C465
Perseus at 610 MHz
Radio sources are - barometers to measure ICM
pressure - anenometers to measure
cluster winds (the only measure so far!)
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Radio relics revived particle pools

• classical cases of peculiar peripheral
  extended radio sources
• - A2256 (Röttgering et al. 1994 Röttgering et
  al. 1994)
• - 1253275 in Coma (Giovannini et al. 1991)
• common properties
• - peripheral
• - steep spectrum
• - linearly polarized ? ordered B-field

A 2256 1465 MHz

• degree p of polarization depends on compression
  ratio of shock, on particle spectrum, N(E) dE
  E-s dE, and on the orientation of shock
  w.r.t. observer

A 2256 opt.
A 2256 X-ray.

• origin of relic several radio galaxies in the
  vicinity of 1253275 (Giovannini et al. 1985)
  ?loss ltlt ?kin solved by large-scale accretion
  shocks (Enßlin et al. 1998) low galaxy density ?
  turbulent reacceleration by galactic wakes ruled
• out.
• 16 clusters with known relics (compilation in
  Slee et al. 2001)
• only 4 clusters with relics have measured
  polarization (see Enßlin et al. 1998).

Coma Cluster 327 MHz
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Cosmological shock waves at intersecting
filaments of galaxies

• NGC315 a giant ( 1.3 Mpc) radio galaxy (GRG)
  with odd radio lobe (Mack 1996 Mack et al.
  1998).
• - morphology precessing jets (Bridle et al.
  1976), but western one with peculiar bend
  towards the host galaxy
• - unusually flat radio spectrum in western lobe
  first steepens (as expected), then flattens to
  ?high ? 0.7 (S? ?--?).
• - strong linear polarization p ? 30.

• Enßlin et al. (2000) originally symmetric radio
  galaxy falling into an intergalactic shock
  wave, along with its environment.
• compression ? reacceleration of particles ?
  strong alignment of magnetic field increased
  synchrotron emissivity

• origin of large-scale gas flow and shock wave?

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• NGC315 located within Pisces-Perseus Supercluster
• Enßlin et al. (2000) identify filaments of
  galaxies with rather different velocity
  dispersions (redshifts from CfA survey, Huchra et
  al. 1990, 1992, 1995)
• - filament I ?v ? 400 km s-1
• - filaments II - V ?v ? 90 220 km s-1
• if gas has comparable ?v , this translates into
• k TI ? 280 eV
• k TII-V ? 15 85 eV

NGC315

• from theory of shocks (Landau Lifschitz 1966)
  ?
• temperature jump T1 /T2 ? 3.3 20
• compression ratio R ? 2.9 3.8
• pressure jump P1 /P2 ? 9.6 75
• ODrury (1983) ? ? ? 0.54 0.79
  expected ?
• N(E) dE E-s dE S? ? -?

I
II
III
IV
V
view from above

• gas in one of smaller filaments (II - IV) may
  get heated by shock wave when flowing into
  deeper gravitational potential of main filament
  (I).
• cosmological shockwave in NGC315 is putative
  onfirmation requires
• - deep X-ray imaging to see heated gas
• - low-frequency search for relic-type, diffuse
  radio emission over entire shock region

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Weather forecast

• head-tail (or other extended) radio sources must
  be studied, along with environment (X-ray
  studies)
• search for radio relics in cluster merger
  candidates at low frequencies, with scrutiny of
  spectral aging and linear polarization
  essentially all cluster merger candidates should
  exhibit this....
• new-generation X-ray telescopes with high
  spatial spectral resolution ? studies of gas
  motions
• to be compared with high-fidelity numerical
  simulations that take advantage from
• - new-generation supercomputers
• - adaptive mesh refinement
• - higher mass resolution
• - MHD

Röttiger et al. 1998
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Landau Lifschitz (1966) pressure and
temperature ratios between down- and upstream
region (inside and outside cluster shock front)
are
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• GRGs probes of tenuous IGM
• Clarke et al. Method (RM in clusters)
• Laing-Garrington
• ram pressure stripping (Virgo)
• how much mass in form of hot gas?
• importance of ghosts?
• primary/secondary/in situ