IMPRS, April 8

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

• 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 ... themes of a commencing graduate school ...

• groups and clusters of galaxies = largest gravitationally boundand collapsed systems in the universe

• groups: 3 ··· 30 galaxies;

• clusters: up to a few 1000

• R ~ 2 Mpc

• M ~ 1014 ··· 1015 M

• groups and clusters of galaxies = largest gravitationally boundand 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

• Local Group: ~ 35 members

• MW, M31, M33; all others dwarf galaxies

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

Clusters of galaxies

• 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 < z < 0.20

• 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 < z < 0.20cD - single dominant cD galaxy (A2029, A2199) B - dominant binary, like Coma F - flattened (IRAS 09104+4109) L - linear array of galaxies (Perseus) C - single core of galaxies I - irregular distribution (Hercules)

50

m1m2

m3 m3+2

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

Structures of galaxy clusters

Coma

A578A1569

belief until ~ mid 80’s: “clusters are simple ...”

however: ample evidence for substructuresubstructure, 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

A3528

Böhringer (1996)

Optical techniques barely disclose gravitational potential in nearby clusters unless these are rich (too few test particles); distant ones: lensing ...

dr

T d

dr

d

m G

r T kr M

H

) (log ) (log) (

2

X-ray morphologies of clusters

Fornax Cluster

11 2 3

r r

GM

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

Abell 2256

• 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

Radio emission from clusters of galaxies

• is the IGM/ICM magnetizied?• how (and when) did it get magnetized?

AGN (‘standard’)dwarf galaxies (Kronberg et al. 1999)

• evidence for B-fields:

Dixit deus: “Fiat lux (campus magnetibusque)”

Another diagnostic tool of cluster physics: radio emission:

synchrotron radiation

- radio halos & relics (e.g. Feretti 1999)

- 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

1

0B Nsyn

I

) ( ) ( ) ( 81 . 0 ,32

kpc

d

G cm

nRM RM

es B

syn

IC

IC

syn IC

I

IB E kT B I I

) 1( 3 ) 1() (

Clarke et al. (1999)

Enßlin & Biermann (1998)

Thierbach et al. (2002)

Feretti & Giovannini (1998)

• radio ‘halos’ : central, diffuse, polarization < 5%

Röttgering et al. (1999)

• radio ‘relics’ : peripheral, 20% polarized

• no obvious particle/energy sources

• steep(ening) spectra at higher frequencies

• how frequemt? many if searched for with scrutiny!

3C465Perseus at 610 MHz

‘Weather stations’ in galaxy clusters

~ 10% of galaxies in clusters produce significant radio synchrotron emission (Pν 1023 W Hz-1 at 20 cm)

• jets of radio plasma ejected from galaxy cores, forming lobes and tails probe relative gas motions over 100’s of kpcs (NATs, WATs)

• however: ~90% of WATs & NATs in clusters with X-raysubstructure; 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 bb (GHz), equipartition magnetic field BBeqeq (G), equivalent magnetic field of CMB BBCMBCMB (G):

j

g ICM j j

r

V

R

V2 2

yrB B

B

CMB eq

eq

b2 2

2/ 1 810

• former belief: tails simply trace ballistic motions of galaxies when radio plasma is exposed to ICM ram pressure (radius of curvature RR , jet radius rrjj , jet velocity

vvjj , galaxy velocity vvgg , density of jet jj , density of ICM ICMICM density of ICM):

Radio sources are

- barometers to measure ICM pressure

- anenometers to measure cluster winds (the only measure so far!)

• classical cases of peculiar peripheral & extended radio sources: - A2256 (Röttgering et al. 1994; Röttgering et al. 1994) - 1253+275 in Coma (Giovannini et al. 1991)

• common properties:- peripheral- steep spectrum- linearly polarized ordered B-field

A 2256 opt.

Radio relics: revived particle pools

• origin of relic: several radio galaxies in the vicinity of 1253+275 (Giovannini et al. 1985); loss loss << kin kin solved by large-scale accretion shocks (Enßlin et al. 1998); low galaxy density turbulent reacceleration by galactic wakes ruledout.

• 16 clusters with known relics (compilation in Slee et al. 2001)

• only 4 clusters with relics have measured polarization (see Enßlin et al. 1998).

) , (3 7

1 R f

s

sp

A 2256 X-ray. Coma Cluster

327 MHz

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:

• 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%.

Cosmological shock waves at intersecting filaments of galaxies

• 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?

• 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

• O’Drury (1983): 0.54 ···· 0.79 expected

N(E) · dE ~ E-s · dE S ~ -

• 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

• 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

view from ‘above’

I II III IV V

NGC315

1

2

R

Rs

‘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

R

R

P

P

4

14

1

2

Landau & Lifschitz (1966): pressure and temperature ratios between down- and upstream region (inside and outside cluster shock front) are:

RP

P

T

T 1

2

1

1

2

• 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