• NGC315: giant (~ 1.3 Mpc) radio galaxy with odd radio lobe (Mack 1996; Mack et al. 1998).

• 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 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

‘view from above’

I II III IV V

NGC315

21

1

R

galaxy clusters contain:• dark matter• hot gas• galaxies • relativistic plasma

work and reviews:Feretti & Giovannini

lifetime of radio structures:

yrBB

B

CMBeq

eq

b 22

2/1810

GzBCMB 2)1(18.3

Thierbach, Klein, Wielebinski (2003)

νb = 0.44 GHzτ = 5.1 · 107 yr

“Halos“ and “relics“:

A2256

Röttgering et al. (1994)

Thierbach (2000)

A3667

Röttgering et al. (1999)

Weather in Perseus

j

gICMjj

r

V

R

V 22

Sijbring (1999)

Nature of radio structuresradio halos (e.g. Coma):• rich clusters with

- 10% spirals- v ~ 1000 km s-1 - LX ~ 1044 1045 erg s-1 - no cooling flows

• central, smooth, extended, 1 Mpc in size• unpolarized• steep radio spectra, break in GHz range

-1.0, Sν ~ ν

origin:• injection of relativistic e- by AGN, starbursts• re-acceleration by galactic wakes• secondary electrons from inelastic collisions between relativistic p and thermal ions

(theory: Enßlin)

radio relics (e.g. A2256):• clusters with substructure• peripheral• strongly polarized (p 20%)• steep radio spectra

~ -0.7 -1.0

origin:• particles deposited by active radio galaxies• shock waves in cluster mergers revive these

(modelling & reviews on theory: Enßlin)

‘mini halos‘ (e.g. M87):• surround dominant central radio galaxies• clusters with cooling flows - particles delivered by radio galaxy

- powered by magneto-hydrodynamic turbulence in cooling core

Filamentary polarized emission in a radio halo (Govoni et al. 2005)A2255 (z = 0.0806)

• high angular resolution• filaments strongly polarized (20% - 40%)• ordered on scales of ~ 400 kpc• B parallel to relic, but perpendicular to filaments!• not a simple picture …

XMM Newton observations of the Coma Cluster relic 1253+275 (Govoni et al. 2005)

O'Drury 1983: spectral index = (M2 + 3) / 2 · (M2 - 1)temp. ratio T1/T2 = (5 M2 – 1) · (M2 + 3) / 16 M2

observed = 1.18 T1/T2 = 2.1• no temperature increase in region of relic seen (X-ray spectra)

radio emission of relic not induced by a shock, but by turbulence?

LOFAR

will

• disclose numerous nonthermal structures in galaxy clusters shed light on structure formation in local universe

• help to understand magnetization of ICM - halos around AGN (radio galaxies, quasars, Seyferts)

- halos around starburst galaxies (dwarfs!!!)

p + p p + n + π+

p + p p + p + π- + π+

π+ μ+ + νμ + e+ + νe + νμ

π- μ- + νμ + e- + νe + νμ

n p + e- + νe