““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?