INTRODUZIONE A: Aloni radio Ammassi di galassie con e senza cool core

1. “Studio della relazione tra presenza di aloni radio e assenza di cool cores in un campione completo di ammassi di galassie” • INTRODUZIONE A: • Aloni radio • Ammassi di galassie con e senza cool core SCOPO DELLA TESINA • METODI: • Il campione di ammassi in radio • Il sottocampione osservato in X

2. COOL CORE vs NON COOL CORE CLUSTERS • CC have more peaked surface brightness (density) distribution Hydra A A3376 EPIC flux images (erg cm-2 s-1) scaled by the maximum value, same scale, same contours levels

3. COOL CORE vs NON COOL CORE CLUSTERS • CC have more peaked surface brightness (density) distribution

4. COOL CORE vs NON COOL CORE CLUSTERS • CC have more peaked surface brightness (density) distribution

5. COOL CORE vs NON COOL CORE CLUSTERS 1e-03 3e-05 1.8e-05 4e-05 5e-02 6e-03 4e-03 5e-03 • CC have more peaked surface brightness (density) distribution

6. COOL CORE vs NON COOL CORE CLUSTERS • CC have DECREASINGtemperature profiles in the inner regions A2199 CC

7. COOL CORE vs NON COOL CORE CLUSTERS • CC have DECREASINGtemperature profiles in the inner regions A3562 NCC

8. COOL CORE vs NON COOL CORE CLUSTERS • CC have DECREASINGtemperature profiles in the inner regions

9. COOL CORE vs NON COOL CORE CLUSTERS • CC have more peaked surface brightness (density) distribution • CC have DECREASINGtemperature profiles in the inner regions • A SIMPLE MODEL: COOLING FLOW! Cluster=sphere of gas in hydrostatic equilibrium Radiation losses cool the gas, more efficiently in the high density regions ( ε~n2). In order to keep hydrostatic pressure, the gas has to increase its density, recalling mass from the outskirts to the center (cooling flow) … BUT THE COOLING FLOW MODEL IS WRONG!! Lack of cool gas below a certain temperature value. Something prevents the gas from cooling (AGN feedback)

10. COOL CORE vs NON COOL CORE CLUSTERS • CC have more peaked surface brightness (density) distribution • CC have DECREASINGtemperature profiles in the inner regions • CC have short cooling time u = energy density ~ nkT ε = bremms emissivity ~n2T1/2 tcool < Hubble time (13.7 Gyr) only in the cores of CC clusters

11. COOL CORE vs NON COOL CORE CLUSTERS • CC have short cooling time

12. COOL CORE vs NON COOL CORE CLUSTERS • CC have lower ENTROPY profiles Specific entropy per particle s=T/n2/3 (keV cm2) Pratt et al., 2009 Entropy profiles in CC are steeper and lower in the inner regions Cool core Non cool core

13. COOL CORE vs NON COOL CORE CLUSTERS • CC have central peaks in Metal Abundance distribution CC NCC The metal abundance central excess is consistent with enrichment from the large elliptical central galaxy (BCG=Brightest Central Galaxy) invariably found in those systems

14. COOL CORE vs NON COOL CORE CLUSTERS • CC have more peaked surface brightness (density) distribution • CC have DECREASINGtemperature profiles in the inner regions • CC have short cooling time • CC have lower ENTROPY profiles • CC have central peaks in Metal Abundance distribution Use these observational features to define indicators of the CC state Good indicators should be effective and easy to calculate

15. COOL CORE vs NON COOL CORE CLUSTERS • CC have more peaked surface brightness (density) distribution • CC have DECREASINGtemperature profiles in the inner regions • CC have short cooling time • CC have lower ENTROPY profiles • CC have central peaks in Metal Abundance distribution Slope of the brightness or density profile at a given radius Temperature drop in the inner region Cooling time at a given radius/central cooling time Central entropy (k0),entropy ratio

16. CLUSTER RADIO EMISSION • Radio galaxies • Extended emission (~Mpc) from the ICM: • (observed only in merging clusters) • Halos • Relics Synchrotron emission from the ICM Presence of RELATIVISTIC PARTICLES and MAGNETIC FIELDS in the ICM The particle acceleration mechanisms are likely related to mergers

17. Synchrotron Radiation (erg s-1 if H in G) (MHz if H in G) RADIO : H = 10-6 G   1000 OPTICAL : H = 1 G   104 X-RAY : H = 10 G   105

18. ENSEMBLE OF ELECTRONS Synchrotron emissivity: Spectral index • AGEING: • only e- with • E < E* survive • spectral break • *  H-3 t -2 Original spectrum Aged spectrum

19. CLUSTER RADIO EMISSION • Radio halos: • Cluster wide diffuse emission • Located at the cluster center • Low surface brightness • (μJy arcsec-2 @1.4 Ghz) • No polarization • Steep radio spectrum COMA CLUSTER ROSAT PSPC (White et al. 1993) Coma Cluster: first cluster where a radio halo was detected α=1 + exponential cutoff HALO Radio 90 cm (Feretti et al. 1998) RELIC Thierbach et al. 2003

20. CLUSTER RADIO EMISSION • Radio relics: • Similar to radio halos but • Located in cluster outskirts • Elongated in shape • Highly polarized A3667 α=1 HALO Radio 90 c Röttgering et al. 1997 Jonhston-Hollit, 2001 Coma relic Thierbach et al. 2003

21. CLUSTER RADIO EMISSION Conditions in radio halos and relics Radio power: ˜ 1024 – 1025 W Hz-1 (@1.4 GHz) Energy density:  10-14-10-13 erg cm-3 lower than the thermal one (10-11-10-12 erg cm-3) Magnetic field: ˜ 0.1 - 1 μG Lorentz factor: γ > 1000 Particle Lifetime: ˜ 108 yr Diffusion velocity: 100 km/s The diffusion velocity of electrons in the ICM is not sufficient to cover Mpc scale distances during their lifetime RELATIVISTIC ELECTRONS NEED TO BE RE-ACCELERATED

22. CLUSTER RADIO EMISSION • How common is extended radio emission in clusters? • The presence of extended radio emission is NOT a common property in galaxy clusters. • Radio halos and relics detected in: • ~10%of a complete X-ray • flux limited sample • ~35% of clusters with • Lx>1045 ergs s-1 • (Giovannini et al 2000, • but possible evolution with z • suggested, Cassano et al.2007) Feretti et al. 2000

23. CLUSTER RADIO EMISSION • ALL cluster containing a radio halo or relic show some indication of recent dynamical activity. We are not presently aware of any radio halo or relic in a cluster where a merger has been clearly excluded • Extended radio emission is probably related to cluster mergers • CAVEAT: not all merging clusters • host a radio halo or relic!! Buote 2001

24. CLUSTER RADIO EMISSION • Extended radio emission is probably related to cluster mergers • Cluster mergers have enough energy to accelerate particles, but what are the acceleration mechanisms? • Shock acceleration (First order Fermi acceleration) • Stochastic acceleration by turbulence following a merger • Secondary Electron production (but not obviously related to merger) Still an open question: no clear correlation between merger shocks and radio halos, unknown turbulence of the ICM

25. CLUSTER FORMATION We now know that the Universe shows a large scale structure, which can be well explained by the hierarchical scenario of structure formation In this scenario, small structures form first, while larger objects are “built” later by the accretion of smaller subunits.

26. SIMULATION OF THE FORMATION OF A GALAXY CLUSTERS Dark Matter only, i.e. Gravity only http://www-theorie.physik.unizh.ch/~moore/movies/expand_wrbb.mpg

27. CLUSTER FORMATION Galaxy clusters are the largest objects in the Universe. In the hierarchical scenario, they form the youngest population: the present is the epoch of cluster formation! Cluster form through the accretion of smaller subunits and the interactions between nearly equal size objects: CLUSTER MERGERS Snapshot from a cosmological simulation

28. CLUSTER FORMATION Cluster mergers are the most energetic events in the Universe since the Big Bang and they can release up to 1064 erg What is the energy involved during a cluster merger? The velocity can be derived assuming a simple model, conserving energy and angular momentum. It depends on the mass of the objects and on the impact parameter. For typical values: v~2000-3000 km/s Sarazin 2001, astro-ph/0105418

29. CLUSTER MERGERS and CC-NCC DISTRIBUTION In this scenario, the CC state is the natural relaxed state to which galaxy clusters evolve. Clusters remain in this state unless disturbed by a merger CC=relaxed object, NCC=interacting object • Cluster mergers drive shock waves and turbulence in the ICM: • They alter the gas distribution and smooth out density (brightness) gradients • They heat the ICM • They mix the gas modifying entropy and metal abundance gradients • They have been suggested as the dominant mechanism to explain the CC-NCC distribution

30. CLUSTER MERGERS and CC-NCC DISTRIBUTION • However, other models have been suggested to explain the CC-NCC distribution, because of • Presence of intermediate peculiar objects • Difficulties in reproducing the observed distribution with numerical simulations • Independent models: primordial division into the two classes (McCarthy et al. 2004, Poole et al 2008, O’Hara et al 2006) • The question is still debated (Sanderson et al. 2009; Leccardi, Rossetti & Molendi, 2009; Rossetti & Molendi, 2009)

31. “Studio della relazione tra presenza di aloni radio e assenza di cool cores in un campione completo di ammassi di galassie” SCOPO DELLA TESINA I dati osservativi e i modelli ci indicano i radio aloni sono legati ai mergers tra ammassi di galassie I mergers sono anche indicati come responsabili della distribuzione di ammassi in CC-NCC in uno dei modelli principali (ma non l’unico!!!) Vogliamo verificare e mettere insieme questi modelli. Gli ammassi con radio alone hanno un cool core? Gli ammassi che non hanno un alone radio (ma che sono abbastanza luminosi in X da poter essere osservabili in radio), come sono distribuiti tra CC e NCC?