introduzione a: aloni radio ammassi di galassie con e senza cool core
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““Studio della relazione tra presenza di aloni radio e Studio della relazione tra presenza di aloni radio e assenza di cool cores in un campione completo di assenza di cool cores in un campione completo di
ammassi di galassie”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
COOL CORE vs NON COOL CORE CLUSTERSCOOL 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
COOL CORE vs NON COOL CORE CLUSTERSCOOL CORE vs NON COOL CORE CLUSTERS
•CC have more peaked surface brightness (density) distribution
COOL CORE vs NON COOL CORE CLUSTERSCOOL CORE vs NON COOL CORE CLUSTERS
•CC have more peaked surface brightness (density) distribution
COOL CORE vs NON COOL CORE CLUSTERSCOOL CORE vs NON COOL CORE CLUSTERS
•CC have more peaked surface brightness (density) distribution
4e-05
1e-03
1.8e-05
3e-05
5e-03
4e-03
5e-02 6e-03
COOL CORE vs NON COOL CORE CLUSTERSCOOL CORE vs NON COOL CORE CLUSTERS
•CC have DECREASING temperature profiles in the inner regions
A2199
CC
COOL CORE vs NON COOL CORE CLUSTERSCOOL CORE vs NON COOL CORE CLUSTERS
•CC have DECREASING temperature profiles in the inner regions
A3562
NCC
COOL CORE vs NON COOL CORE CLUSTERSCOOL CORE vs NON COOL CORE CLUSTERS
•CC have DECREASING temperature profiles in the inner regions
COOL CORE vs NON COOL CORE CLUSTERSCOOL CORE vs NON COOL CORE CLUSTERS
•CC have more peaked surface brightness (density) distribution
•CC have DECREASING temperature profiles in the inner regions
A SIMPLE MODEL: COOLING FLOWCOOLING 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!!BUT THE COOLING FLOW MODEL IS WRONG!!
Lack of cool gas below a certain temperature value. Something prevents the gas from cooling (AGN feedback)
COOL CORE vs NON COOL CORE CLUSTERSCOOL CORE vs NON COOL CORE CLUSTERS
•CC have more peaked surface brightness (density) distribution
•CC have DECREASING temperature profiles in the inner regions
•CC have short cooling time
u = energy density ~ nkT
ε = bremms emissivity ~n2T1/2
2/11gpcool Tn
ut
2/1
8
1
3310
1010105.8
K
T
cm
nyrt gp
cool
tcool < Hubble time (13.7 Gyr) only in the cores of CC clusters
COOL CORE vs NON COOL CORE CLUSTERSCOOL CORE vs NON COOL CORE CLUSTERS
•CC have short cooling time
2/1
8
1
3310
1010105.8
K
T
cm
nyrt gp
cool
COOL CORE vs NON COOL CORE CLUSTERSCOOL 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
Cool core
Non cool core
Entropy profiles in CC are steeper and lower in the inner regions
COOL CORE vs NON COOL CORE CLUSTERSCOOL CORE vs NON COOL CORE CLUSTERS
•CC have central peaks in Metal Abundance distribution
The metal abundance central excess is consistent with enrichment from the large elliptical central galaxy (BCG=Brightest Central Galaxy) invariably found in those systems
CC
NCC
COOL CORE vs NON COOL CORE CLUSTERSCOOL CORE vs NON COOL CORE CLUSTERS
•CC have more peaked surface brightness (density) distribution•CC have DECREASING temperature 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
COOL CORE vs NON COOL CORE CLUSTERSCOOL CORE vs NON COOL CORE CLUSTERS
•CC have more peaked surface brightness (density) distribution
•CC have DECREASING temperature 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
•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
CLUSTER RADIO EMISSIONCLUSTER RADIO EMISSION
H
Hdt
dE
s2
2215
2.4
106.1
(erg s-1 if H in G)
(MHz if H in G)
Synchrotron Radiation Synchrotron Radiation
RADIO : H = 10-6 G 1000
OPTICAL : H = 1 G 104
X-RAY : H = 10 G 105
2/)1(
0HN ENEN 0)(
2
1
ENSEMBLE OF ELECTRONS
Synchrotron emissivity:
Original spectrum Aged spectrum
Spectral index
AGEING: only e- with E < E* survive spectral break
* H-3 t -2
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
CLUSTER RADIO EMISSIONCLUSTER RADIO EMISSION
ROSAT PSPC
(White et al. 1993)
Radio 90 cm
(Feretti et al. 1998)
COMA CLUSTER
HALO
RELIC
Coma Cluster: first cluster where a radio halo was detected
Thierbach et al. 2003
α=1 + exponential cutoff
Radio relics:
Similar to radio halos but•Located in cluster outskirts•Elongated in shape•Highly polarized
CLUSTER RADIO EMISSIONCLUSTER RADIO EMISSION
Radio 90 cHALO
α=1
Thierbach et al. 2003
Coma relic
Röttgering et al. 1997
Jonhston-Hollit, 2001
A3667
Particle Lifetime:
˜ 108 yr
Diffusion velocity:100 km/s
Particle Lifetime:
˜ 108 yr
Diffusion velocity:100 km/s
Radio power: ˜ 1024 – 1025 W Hz-1 (@1.4 GHz)Radio power: ˜ 1024 – 1025 W Hz-1 (@1.4 GHz)
Magnetic field: ˜ 0.1 - 1 μG
Lorentz factor: γ > 1000
Magnetic field: ˜ 0.1 - 1 μG
Lorentz factor: γ > 1000
Conditions in radio halos and relicsConditions in radio halos and relics
Energy density: 10-14-10-13 erg cm-3
lower than the thermal one (10-11-10-12 erg cm-3)
Energy density: 10-14-10-13 erg cm-3
lower than the thermal one (10-11-10-12 erg cm-3)
CLUSTER RADIO EMISSIONCLUSTER RADIO EMISSION
The diffusion velocity of electrons in the ICM is not sufficient to cover Mpc scale distances during their lifetimeRELATIVISTIC ELECTRONS NEED TO BE RE-ACCELERATED
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)
CLUSTER RADIO EMISSIONCLUSTER RADIO EMISSION
Feretti et al. 2000
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 excludedExtended radio emission is probably related to cluster mergers
CAVEAT: not all merging clustershost a radio halo or relic!!
CLUSTER RADIO EMISSIONCLUSTER RADIO EMISSION
Buote 2001
Extended radio emission is probably related to cluster mergers
Cluster mergers have enough energy to accelerate particles, but what are the acceleration mechanisms?
CLUSTER RADIO EMISSIONCLUSTER RADIO EMISSION
•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
CLUSTER FORMATIONCLUSTER 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.
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
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
CLUSTER FORMATIONCLUSTER 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
CLUSTER FORMATIONCLUSTER FORMATION
Sarazin 2001, astro-ph/0105418
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
CLUSTER MERGERS and CC-NCC CLUSTER MERGERS and CC-NCC DISTRIBUTIONDISTRIBUTION
However, other models have been suggested to explain the CC-NCC distribution, because of
1. Presence of intermediate peculiar objects
2. 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)
CLUSTER MERGERS and CC-NCC CLUSTER MERGERS and CC-NCC DISTRIBUTIONDISTRIBUTION
““Studio della relazione tra presenza di aloni radio e Studio della relazione tra presenza di aloni radio e assenza di cool cores in un campione completo di assenza di cool cores in un campione completo di
ammassi di galassie”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?
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