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Introduction to dark matterIndirect dark matter searches
High-energy phenomena
High-Energy Phenomena and Dark MatterSearches in Galaxy Clusters
Christoph Pfrommer1
in collaboration with
Anders Pinzke2, Lars Bergström2,Torsten Enßlin3, Volker Springel3
1Canadian Institute for Theoretical Astrophysics, Canada2Stockholm University, Sweden
3Max-Planck Institute for Astrophysics, Germany
Nov 25, 2009 / McMaster University
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Outline
1 Introduction to dark matterProperties of dark matterTheory and observationsRecent exciting developments
2 Indirect dark matter searchesOur approachGamma-ray signaturesImplications for cosmological structure formation
3 High-energy phenomenaCosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Properties of dark matterTheory and observationsRecent exciting developments
Outline
1 Introduction to dark matterProperties of dark matterTheory and observationsRecent exciting developments
2 Indirect dark matter searchesOur approachGamma-ray signaturesImplications for cosmological structure formation
3 High-energy phenomenaCosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Properties of dark matterTheory and observationsRecent exciting developments
Properties of dark matterWhat have galaxy clusters taught us about dark matter?
Dark matter exists and is . . .
. . . gravitationally interacting: most of the matter in the Universeis dark (galaxy clusters, galactic rotation curves, gravitationallensing, CMB, . . . )
. . . cold: it was non-relativistic at the time of decoupling fromweak interactions – otherwise structure formation would haveproceeded ‘top-down’, in contrast to our hierarchical structureformation scenario (Ly-α forest, structure formation)
. . . non-baryonic: it does not interact electro-magnetically withordinary matter (CMB + structure formation)
. . . collisionless: it has a very weak self-interaction cross section(galaxy clusters, relic density)
→ dark matter is a weakly interacting massive particle (WIMP), butwhat is it really (SUSY, extra dimensions, . . . )?
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Properties of dark matterTheory and observationsRecent exciting developments
The matter content of the Universe – 2009
WMAP Five-Year: Komatsu et al. (2009)
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Properties of dark matterTheory and observationsRecent exciting developments
Zwicky: first evidence for dark matter
Zwicky (1933) applied the virial theorem to theComa cluster of galaxies:
Egrav + 2Ekin = 0
Ekin: energy based on galaxies motions,Egrav: estimated gravitational energy
Zwicky found about 400 times more estimatedmass than visually observable
“missing mass problem”: the gravity of the visible galaxies in thecluster would be far too small for such fast orbits:
→ there must be some non-visible form of matter that providesenough of the mass and gravity to hold the cluster together
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Properties of dark matterTheory and observationsRecent exciting developments
Properties of dark matterWhat have galaxy clusters taught us about dark matter?
Dark matter exists and is . . .
. . . gravitationally interacting: most of the matter in the Universeis dark (galaxy clusters, galactic rotation curves, gravitationallensing, CMB, . . . )
. . . cold: it was non-relativistic at the time of decoupling fromweak interactions – otherwise structure formation would haveproceeded ‘top-down’, in contrast to our hierarchical structureformation scenario (Ly-α forest, structure formation)
. . . non-baryonic: it does not interact electro-magnetically withordinary matter (CMB + structure formation)
. . . collisionless: it has a very weak self-interaction cross section(galaxy clusters, relic density)
→ dark matter is a weakly interacting massive particle (WIMP), butwhat is it really (SUSY, extra dimensions, . . . )?
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Properties of dark matterTheory and observationsRecent exciting developments
Properties of dark matterWhat have galaxy clusters taught us about dark matter?
Dark matter exists and is . . .
. . . gravitationally interacting: most of the matter in the Universeis dark (galaxy clusters, galactic rotation curves, gravitationallensing, CMB, . . . )
. . . cold: it was non-relativistic at the time of decoupling fromweak interactions – otherwise structure formation would haveproceeded ‘top-down’, in contrast to our hierarchical structureformation scenario (Ly-α forest, structure formation)
. . . non-baryonic: it does not interact electro-magnetically withordinary matter (CMB + structure formation)
. . . collisionless: it has a very weak self-interaction cross section(galaxy clusters, relic density)
→ dark matter is a weakly interacting massive particle (WIMP), butwhat is it really (SUSY, extra dimensions, . . . )?
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Properties of dark matterTheory and observationsRecent exciting developments
Evidence for non-baryonic dark mattertemperature fluctuations the epoch of recombination (z ' 1100)have an amplitude δT/T ' 10−5
linear regime of structure formation: δ(z) ∝ 1/(1 + z)
if dark matter were baryonic, we would only have time to growfluctuations of size δ ' 10−2
since we observe galaxies with δ & 102, dark matter fluctuationsmust have started to grow before recombination which is onlypossible if dark matter does not interact electro-magneticallywith matter
NASA/WMAP: 5 year CMB sky
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Properties of dark matterTheory and observationsRecent exciting developments
Properties of dark matterWhat have galaxy clusters taught us about dark matter?
Dark matter exists and is . . .
. . . gravitationally interacting: most of the matter in the Universeis dark (galaxy clusters, galactic rotation curves, gravitationallensing, CMB, . . . )
. . . cold: it was non-relativistic at the time of decoupling fromweak interactions – otherwise structure formation would haveproceeded ‘top-down’, in contrast to our hierarchical structureformation scenario (Ly-α forest, structure formation)
. . . non-baryonic: it does not interact electro-magnetically withordinary matter (CMB + structure formation)
. . . collisionless: it has a very weak self-interaction cross section(galaxy clusters, relic density)
→ dark matter is a weakly interacting massive particle (WIMP), butwhat is it really (SUSY, extra dimensions, . . . )?
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Properties of dark matterTheory and observationsRecent exciting developments
Evidence for collisionless dark matter
1E 0657-56 (“Bullet cluster”)(X-ray: NASA/CXC/CfA/M.Markevitch et al.; Optical:NASA/STScI; Magellan/U.Arizona/D.Clowe et al.; Lensing:NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al.)
red: X-ray emittingcluster plasma
blue: weak lensing(dark matter) map
yellow: galaxies
the (collisionless) galaxiesfollow the dark matter distri-bution, the bulk of the plasmalags behind
→ dark matter is collisionless
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Properties of dark matterTheory and observationsRecent exciting developments
Properties of dark matterWhat have galaxy clusters taught us about dark matter?
Dark matter exists and is . . .
. . . gravitationally interacting: most of the matter in the Universeis dark (galaxy clusters, galactic rotation curves, gravitationallensing, CMB, . . . )
. . . cold: it was non-relativistic at the time of decoupling fromweak interactions – otherwise structure formation would haveproceeded ‘top-down’, in contrast to our hierarchical structureformation scenario (Ly-α forest, structure formation)
. . . non-baryonic: it does not interact electro-magnetically withordinary matter (CMB + structure formation)
. . . collisionless: it has a very weak self-interaction cross section(galaxy clusters, relic density)
→ dark matter is a weakly interacting massive particle (WIMP), butwhat is it really (SUSY, extra dimensions, . . . )?
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Properties of dark matterTheory and observationsRecent exciting developments
The WIMP miracle
Fermi introduced a new mass scaleof mweak ∼ 100 GeV to describe thebeta decay: n → p e− ν
assuming a new (heavy) particle X ,initially in thermal equilibrium, with arelic density
ΩX ∼1
mPlT0 〈συ〉∼
m2X
mPlT0 g4X
mx ∼ mweak ∼ 100 GeVgx ∼ gweak ∼ 0.6
ΩX ∼ 0.1
Remarkable coincidence: particle physics independentlypredicts particles with the right density to be dark matter
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Properties of dark matterTheory and observationsRecent exciting developments
WIMP detection
Correct relic density → DM annihilation in the Early Universe
q
indiect detection
DM
pro
duct
ion
now
:pa
rtic
le c
ollid
ers
DM scattering now:direct detection
χ χ
q
DM
annihilation now:
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Properties of dark matterTheory and observationsRecent exciting developments
Indirect detection of dark matter
νeν_µ
νe
e+
Springel et al. 2008
Supersymmetric
χµ−
µ+
e−χneutralinos
νµ
_
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Properties of dark matterTheory and observationsRecent exciting developments
Indirect detection of dark matter
νeν_µ
νe
e+
H.E.S.S.
neutralinos
νµ
_
Supersymmetric
PAMELA
Fermi
χµ−
µ+
e−χ
and cooling:limiting horizon ~ 1 kpc
Diffusive transport
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Properties of dark matterTheory and observationsRecent exciting developments
Imaging air Cerenkov telescopes – the technique (1)
high-energy γ-ray impacts the Earth’s atmosphere and sets offan electro-magnetic cascade in the vicinity of a nucleus
e+/e− travel faster than the speed of light in the atmosphere →emission of a cone of blue Cerenkov light
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Properties of dark matterTheory and observationsRecent exciting developments
Imaging air Cerenkov telescopes – the technique (2)
primary γ-rays and hadrons cause different showercharacteristics → separation of γ-rays from ‘background’ events
opening angle and shower location in the shower image allowsreconstructing the initial energy and direction of the γ-ray
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Properties of dark matterTheory and observationsRecent exciting developments
PAMELA and HESS data on electrons and positrons
Energy (GeV)
1 10 100
))
-(e!
)+
+(e!
) /
(+
(e!
Po
sit
ron
fra
cti
on
0.01
0.02
0.1
0.2
0.3
PAMELA
PAMELA: (Adriani et al. 2009)
rising positron fraction with energy→ e−/e+ pair acceleration source
Energy (GeV)210 310
)-1
sr
-1 s
-2 m2
dN
/dE
(G
eV3
E
210
15%± E ∆
ATICPPB-BETSKobayashi
H.E.S.S.H.E.S.S. - low-energy analysisSystematic errorSystematic error - low-energy analysis Broken power-law fit
HESS: (Aharonian et al. 2009)
break in the e−/e+ spectrum→ maximum voltage of acceleratoror DM particle mass
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Properties of dark matterTheory and observationsRecent exciting developments
Combining recent electron and positron dataFermi: excess number of leptons compared to background model (Abdo et al. 2009)
Bergström, Edsjö & Zaharijas 2009
MDM = 1.6 TeV, 100% μ+μ-, EF=1100
FermiHESS (×0.85)HESS LE (×0.85)TotalBackground (×0.85)DM signal
E3 Φ [
GeV
2 m
-2 s
-1 s
r-1]
10
100
Positron energy, Ee+ [GeV]100 1000
PAMELA
Posi
tro
n fr
acti
on
0.01
0.1
Ee+ [GeV]10 100
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Properties of dark matterTheory and observationsRecent exciting developments
Interpretations of recent electron and positron data
excess number of leptons comparedto background (Fermi/HESS)
break in the e−/e+ spectrumindicates special energy scale(HESS)
rising positron fraction with energy(PAMELA)
Bergström, Edsjö & Zaharijas 2009
MDM = 1.6 TeV, 100% μ+μ-, EF=1100
FermiHESS (×0.85)HESS LE (×0.85)TotalBackground (×0.85)DM signal
E3 Φ [
GeV
2 m
-2 s
-1 s
r-1]
10
100
Positron energy, Ee+ [GeV]100 1000
PAMELA
Posi
tro
n fr
acti
on
0.01
0.1
Ee+ [GeV]10 100
1.) nearby pulsars:energetics convincing but smoothness of Fermi data was claimed tobe difficult to model (Harding & Ramaty 1987, Aharonian et al 1995, Malyshev et al. 2009)
2.) DM annihilations:excellent fit to data but enhancement of cross-section over standardvalue and muon decay channel necessary (Bergström et al. 2009)
→ Sommerfeld enhancement: 〈συ〉 ∼ c/υ (Arkani-Hamed et al. 2009)
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Our approachGamma-ray signaturesImplications for cosmological structure formation
Outline
1 Introduction to dark matterProperties of dark matterTheory and observationsRecent exciting developments
2 Indirect dark matter searchesOur approachGamma-ray signaturesImplications for cosmological structure formation
3 High-energy phenomenaCosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Our approachGamma-ray signaturesImplications for cosmological structure formation
The key questions
How can we test this scenario?
Which are the most promising objects to target?
What are the cosmological implications of such an effective darkmatter annihilation?
I will argue in favor of gamma-ray observations of galaxy clustersbeing able to scrutinize the DM interpretation ofFermi/HESS/PAMELA data and will end with a surprisingcosmological result.
Pinzke, CP, Bergström, Phys. Rev. Lett., 2009, 103, 181302
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Our approachGamma-ray signaturesImplications for cosmological structure formation
The key questions
How can we test this scenario?
Which are the most promising objects to target?
What are the cosmological implications of such an effective darkmatter annihilation?
I will argue in favor of gamma-ray observations of galaxy clustersbeing able to scrutinize the DM interpretation ofFermi/HESS/PAMELA data and will end with a surprisingcosmological result.
Pinzke, CP, Bergström, Phys. Rev. Lett., 2009, 103, 181302
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Our approachGamma-ray signaturesImplications for cosmological structure formation
Dissecting the dark matter flux
Nγ =
[∫LOS
ρ2χ dlχ
]〈συ〉2M2
χ
[ ∫ Mχ
Eth
(dNγ
dE
)SUSY
Aeff(E) dE]
∆Ω
4πτexp
astrophysics: contains the uncertainty about the DM profile withits central behavior and the substructure distribution
particle physics: assuming DM is supersymmetric, there is theuncertainty about the cross section, neutralino mass, and decaychannels
detector properties: energy dependent effective area, detectorresponse, scanning strategy, . . .
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Our approachGamma-ray signaturesImplications for cosmological structure formation
Boost factors
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Our approachGamma-ray signaturesImplications for cosmological structure formation
Galaxy clusters vs. dwarf galaxiesWhy look for clusters in the γ-ray band?
1 The DM annihilation flux of the smooth halo component scalesas F ∼
∫dVρ2/D2 ∼ M/D2 assuming a universal density
scaling1: the smooth component of dwarfs and galaxy clustersare equally bright!
2 Substructure in dark matter halos is less concentrated comparedto the smooth halo component (dynamical friction, tidal heatingand disruption): the DM luminosity is dominated by substructureat the virial radius, IF present!→ these regions are tidally stripped in dwarf galaxies→ galaxy clusters are dynamically ‘young’ and their subhalopopulation can boost the DM luminosity by up to 200(Springel et al. 2008).
1A more refined argument that takes into account the different haloformation epochs breaking scale invariance yields the same result.
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Our approachGamma-ray signaturesImplications for cosmological structure formation
Indirect detection of DM through gamma-rays
νeν_µ
νe
e+
χµ−
µ+
e−χneutralinos
νµ
_
Supersymmetric
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Our approachGamma-ray signaturesImplications for cosmological structure formation
Indirect detection of DM through gamma-rays
νeν_µ
νe
e+
radiation
χ
γ
µ−
Final state
µ+
e−χneutralinos
νµ
_
Supersymmetric
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Our approachGamma-ray signaturesImplications for cosmological structure formation
Indirect detection of DM through gamma-rays
νeν_µ
νe
e+
radiation
_
Supersymmetric
χ
γ
µ−
Final state
µ+
e−
γ Compton
χCMBneutralinos
Inverse νµ
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Our approachGamma-ray signaturesImplications for cosmological structure formation
Gamma-ray spectrum from DM annihilations
10-1 100 101 102 103
E γ [GeV]
10-11
10-10
10-9
E γ
2 d
F/dE
[ G
eV c
m-2
s-1
]
FornaxDM-IC-SFEDM-FSR-SFE
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Our approachGamma-ray signaturesImplications for cosmological structure formation
Gamma-ray spectrum from DM vs. CR interactions
10-1 100 101 102 103
E γ [GeV]
10-11
10-10
10-9
E γ
2 d
F/dE
[ G
eV c
m-2
s-1
]
FornaxDM-IC-SFEDM-FSR-SFECR- π 0
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Our approachGamma-ray signaturesImplications for cosmological structure formation
Gamma-ray spectrum for various galaxy clusters
10-1 100 101 102 103
E γ [GeV]
10-11
10-10
10-9
E γ
2 d
F/dE
[ G
eV c
m-2
s-1
]
FornaxComaVirgo
DM-IC-SFEDM-FSR-SFECR- π 0
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Our approachGamma-ray signaturesImplications for cosmological structure formation
DM gamma-rays: without substructure
10-1 100 101 102 103
E γ [GeV]
10-12
10-11
10-10
10-9
10-8
E γ
2 d
F/dE
[ G
eV c
m-2
s-1
]
Fornax:
Cl. w/o SubB
DM-SFE
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Our approachGamma-ray signaturesImplications for cosmological structure formation
DM gamma-rays: with substructure
10-1 100 101 102 103
E γ [GeV]
10-12
10-11
10-10
10-9
10-8
E γ
2 d
F/dE
[ G
eV c
m-2
s-1
]
Fornax:
Cl. w/ SubBCl. w/o SubB
DM-SFE
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Our approachGamma-ray signaturesImplications for cosmological structure formation
DM gamma-rays: with substructure and Milky Way
10-1 100 101 102 103
E γ [GeV]
10-12
10-11
10-10
10-9
10-8
E γ
2 d
F/dE
[ G
eV c
m-2
s-1
]
Fornax:Cl. w/ SubB + MWCl. w/ SubBCl. w/o SubB
DM-SFE
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Our approachGamma-ray signaturesImplications for cosmological structure formation
Probing small scales with gamma-rays
10-1 100 101 102 103
E γ [GeV]
10-14
10-13
10-12
10-11
10-10
10-9
10-8
F (
> E
γ )
[ p
h cm
-2 s
-1]
Virgo: 5.8deg, 5x10 -3MO •
FERMI
EGRET
DM-SFECR- π 0
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Our approachGamma-ray signaturesImplications for cosmological structure formation
Implications for cosmological structure formationProbing the linear power spectrum on the smallest scales
−2 −6
log
10
CDM prediction(Hofmann et al. 2002)
limit obtained by EGRETnon−detection of Virgo(Pinzke, CP, Bergstrom 2009)
upper limit byLy− forest(Seljak et al. 2006)
2 x 108
lower limit possiblewith Fermi sensitivity
M / Msol
k x kpc
P ~ k−3P
α
630300.60.001
103
10
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Our approachGamma-ray signaturesImplications for cosmological structure formation
Conclusions on dark matter searches
Gamma-ray observations of galaxy clusters by Fermi will test theDM interpretation of the Fermi/HESS/PAMELA data in the nextyears.
If the DM interpretation is correct, then we either live in a warmdark matter Universe or there is a new dynamical effect duringnon-linear structure formation that wipes out the smalleststructures.
Gamma-ray observations might be the most sensitive probes ofthe smallest cosmological structures.
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Outline
1 Introduction to dark matterProperties of dark matterTheory and observationsRecent exciting developments
2 Indirect dark matter searchesOur approachGamma-ray signaturesImplications for cosmological structure formation
3 High-energy phenomenaCosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Shocks in galaxy clusters
1E 0657-56 (“Bullet cluster”)(X-ray: NASA/CXC/CfA/M.Markevitch et al.; Optical:NASA/STScI; Magellan/U.Arizona/D.Clowe et al.; Lensing:NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al.)
Abell 3667(radio: Johnston-Hollitt. X-ray: ROSAT/PSPC.)
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Radiative cool core cluster simulation: gas density
10-1
100
101
102
-15 -10 -5 0 5 10 15-15
-10
-5
0
5
10
15
-15 -10 -5 0 5 10 15x [ h-1 Mpc ]
-15
-10
-5
0
5
10
15
y [
h-1 M
pc ]
-15 -10 -5 0 5 10 15-15
-10
-5
0
5
10
15
〈1+δ
gas〉
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Mass weighted temperature
105
106
107
108
-15 -10 -5 0 5 10 15-15
-10
-5
0
5
10
15
-15 -10 -5 0 5 10 15x [ h-1 Mpc ]
-15
-10
-5
0
5
10
15
y [
h-1 M
pc ]
-15 -10 -5 0 5 10 15-15
-10
-5
0
5
10
15
〈Tρ
gas〉/〈ρ
gas〉
[K]
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Mach number distribution weighted by εdiss
1
10
-15 -10 -5 0 5 10 15-15
-10
-5
0
5
10
15
-15 -10 -5 0 5 10 15x [ h-1 Mpc ]
-15
-10
-5
0
5
10
15
y [ h
-1 M
pc ]
-15 -10 -5 0 5 10 15-15
-10
-5
0
5
10
15
〈Mε
diss/〈ε
diss〉
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Radiative simulations – flowchart
CP, Enßlin, Springel (2008)
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Collisionless shocks at supernova remnants
Astrophysical collisionless shocks can:
accelerate particles (electrons and ions)
amplify magnetic fields (or generate them from scratch)
exchange energy between electrons and ions
SN 1006 X-rays (CXC/Hughes) G347.3 HESS TeV(Aharonian et al. 2006)
Tycho X-rays (CXC)
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Diffusive shock acceleration – Fermi 1 mechanism
Spectral index depends on the Mach number of the shock,M = υshock/cs:
log p
strong shock
10 GeV
weak shock
keV
log f
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Radiative simulations with cosmic ray (CR) physics
CP, Enßlin, Springel (2008)
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Radiative simulations with extended CR physics
CP, Enßlin, Springel (2008)
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Radiative simulations with extended CR physics
CP, Enßlin, Springel (2008)
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Hadronic cosmic ray proton interaction
π0
π+
µ+
νµ
ν_µ
νe
p
CRp
e+
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Hadronic cosmic ray proton interaction
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Mach number distribution weighted by εdiss
1
10
-15 -10 -5 0 5 10 15-15
-10
-5
0
5
10
15
-15 -10 -5 0 5 10 15x [ h-1 Mpc ]
-15
-10
-5
0
5
10
15
y [ h
-1 M
pc ]
-15 -10 -5 0 5 10 15-15
-10
-5
0
5
10
15
〈Mε
diss/〈ε
diss〉
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Mach number distribution weighted by εCR,inj
1
10
-15 -10 -5 0 5 10 15-15
-10
-5
0
5
10
15
-15 -10 -5 0 5 10 15x [ h-1 Mpc ]
-15
-10
-5
0
5
10
15
y [ h
-1 M
pc ]
-15 -10 -5 0 5 10 15-15
-10
-5
0
5
10
15
〈Mε
CR,in
j〉/〈ε
CR,in
j〉
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
CR pressure PCR
10-17
10-16
10-15
10-14
10-13
10-12
-15 -10 -5 0 5 10 15-15
-10
-5
0
5
10
15
-15 -10 -5 0 5 10 15x [ h-1 Mpc ]
-15
-10
-5
0
5
10
15
y [
h-1 M
pc ]
-15 -10 -5 0 5 10 15-15
-10
-5
0
5
10
15
〈PC
Rρ
gas〉/〈ρ
gas〉
[erg
cm−
3h2 70
]
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Multi messenger approach for non-thermal processes
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Multi messenger approach for non-thermal processes
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Multi messenger approach for non-thermal processes
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Multi messenger approach for non-thermal processes
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Hadronic γ-ray emission, Eγ > 100 GeV
10-12
10-11
10-10
10-9
10-8
S γ (
Eγ >
100
GeV
) [
ph c
m-2
s-1
]
-5 0 5
-5
0
5
-8 -6 -4 -2 0 2 4 6 8x [ Mpc ]
-8
-6
-4
-2
0
2
4
6
8
y [
Mpc
]
-8 -6 -4 -2 0 2 4 6 8-8
-6
-4
-2
0
2
4
6
8
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Inverse Compton emission, EIC > 100 GeV
10-12
10-11
10-10
10-9
10-8
S IC
,tota
l (E
γ > 1
00 G
eV)
[ ph
cm
-2 s
-1 ]
-5 0 5
-5
0
5
-8 -6 -4 -2 0 2 4 6 8x [ Mpc ]
-8
-6
-4
-2
0
2
4
6
8
y [
Mpc
]
-8 -6 -4 -2 0 2 4 6 8-8
-6
-4
-2
0
2
4
6
8
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Total γ-ray emission, Eγ > 100 GeV
10-12
10-11
10-10
10-9
10-8
S tot
al (
Eγ >
100
GeV
) [
ph c
m-2
s-1
]
-5 0 5
-5
0
5
-8 -6 -4 -2 0 2 4 6 8x [ Mpc ]
-8
-6
-4
-2
0
2
4
6
8
y [
Mpc
]
-8 -6 -4 -2 0 2 4 6 8-8
-6
-4
-2
0
2
4
6
8
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
CR proton and γ-ray spectrum (Pinzke & CP 2009)
10-2 100 102 104 106 108
p = Pp / (mp c)
10-3
10-2
10-1
1.0
f(p)
p2
10-2 100 102 104 106 108 1010
Eγ [ GeV ]
10-12
10-11
10-10
10-9
Fγ(>
Eγ)Eγ
[GeV
cm−
2s−
1]
sIC
pIC
Pion decay
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Universal CR spectrum in clusters
GLAST: ~ 2.4
IACT: ~ 2.2αp
pα
10-4 10-2 100 102 104 106 108 1010
p
0.001
0.01
0.1
1
10
< f(
p) p
2 >
Normalized CR spectrum shows universal concave shape→ governed byhierarchical structure formation and the implied distribution of Mach numbersthat a fluid element had to pass through in cosmic history (Pinzke & CP 2009).
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Gamma-ray scaling relations
1014 1015
Mvir [ MO • ]
1041
1042
1043
1044
1045
1046L
γ (E
γ > 1
00 M
eV)
[ ph
s-1
]total γ-ray emission, excl. galaxies, R<Rvirpion-decay γ-ray emissionprimary IC emissionsecondary IC emission
Scaling relation + complete sample of the brightest X-ray clusters(HIFLUGCS)→ predictions for Fermi and IACT’s
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Predicted cluster sample for Fermi and IACT’s
0 20 40 60 80 100
10-10
10-9
10-8
0 20 40 60 80 100
10-13
10-12
10-10
10-9
10-8
OPHIUCHU
COMA
FORNAX
A3627
PERSEUS
A3526
A1060
3C129
AWM7
M49
A0754
CRs with galaxiesCRs witout galaxies
Fγ(Eγ>
100
GeV
)
Fγ(Eγ>
100
MeV
)
extended HIFLUGCS cluster ID
black: optimistic model, including galactic ‘point sources’ that bias γ-ray fluxhigh; red: realistic model, excluding galactic ‘point sources’
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Predicted cluster sample for Fermi – brightest objects
10-10 10-9 10-80
2
4
6
8
10
12
14 excl. galaxies
Oph
iuch
us
Coma
A36
27, P
erse
us
Forn
ax
A36
26, A
1060
3C12
9
Ncl
uste
rs
Fγ [ph cm−2 s−1]
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
MAGIC observations of Perseus
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Upper limit on the TeV γ-ray emission from Perseus
100 1000E [GeV]
10-14
10-13
10-12
10-11
10-10F
γ ( >
E )
[ph
s-1
cm
-2]
radiative physics w/ gal. x 3.5
radiative physics w/ gal.
radiative physics w/o gal.
Fγ, min (B0 = 10 µG, εB < εth / 3)
The MAGIC Collaboration: Aleksic et al. & CP et al. 2009
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Results from the Perseus observation by MAGIC
assuming f ∝ p−α with α = 2.1, PCR ∝ Pth:ECR < 0.017Eth → most stringent constraint on CR pressure!
upper limits consistent with cosmological simulations:Fupper limits(100GeV ) = 3.5 Fsim (optimistic model)
simulation modeling of pressure constraint yields〈PCR〉/〈Pth〉 < 0.07 (0.14) for the core (entire cluster)
3 physical effects that resolve the apparent discrepancy:
concave curvature ‘hides’ CR pressure at GeV energiesgalactic ‘point sources’ bias γ-ray flux high and pressurelimits low (partly physical)relative CR pressure increases towards the outer parts(adiabatic compression and softer equation of state of CRs)
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Minimum γ-ray flux in the hadronic model
0.1 1.0 10.010-3
10-2
10-1
100
101
B[µG]
j ν,I
C(B
)/j ν,I
C(B
CM
B)
jν(B)/ jν(BCMB)
jIC(B)/ jIC(BCMB)
For jν(B) :αν = 1αν = 1.15αν = 1.30αν = 1.45
Synchrotron emissivity of high-energy, steady state electrondistribution is independent of themagnetic field for B BCMB!
Synchrotron luminosity:
Lν = Aν
∫dV nCRngas
ε(αν+1)/2B
εCMB + εB
→ Aν
∫dV nCRngas (εB εCMB)
γ-ray luminosity:
Lγ = Aγ
∫dV nCRngas
→ minimum γ-ray flux:
Fγ,min =Aγ
Aν
Lν
4πD2
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Minimum γ-ray flux in the hadronic model
0.1 1.0 10.010-3
10-2
10-1
100
101
B[µG]
j ν,I
C(B
)/j ν,I
C(B
CM
B)
jν(B)/ jν(BCMB)
jIC(B)/ jIC(BCMB)
For jν(B) :αν = 1αν = 1.15αν = 1.30αν = 1.45
Synchrotron emissivity of high-energy, steady state electrondistribution is independent of themagnetic field for B BCMB!
Synchrotron luminosity:
Lν = Aν
∫dV nCRngas
ε(αν+1)/2B
εCMB + εB
→ Aν
∫dV nCRngas (εB εCMB)
γ-ray luminosity:
Lγ = Aγ
∫dV nCRngas
→ minimum γ-ray flux:
Fγ,min =Aγ
Aν
Lν
4πD2
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Minimum γ-ray flux in the hadronic model: Fermi
Minimum γ-ray flux (Eγ > 100 MeV) for the Coma cluster:
CR spectral index 2.0 2.3 2.6 2.9Fγ [10−10 ph cm−2s−1] 0.8 1.6 3.4 7.1
These limits can be made even tighter when considering energyconstraints, PB < Pgas/30 and B-fields derived from Faradayrotation studies, B0 = 3 µG:Fγ,COMA & (1.1 . . . 1.5)× 10−9γ cm−2s−1 . FFermi, 2yr
Non-detection by Fermi seriously challenges the hadronicmodel.
Potential of measuring the CR acceleration efficiency fordiffusive shock acceleration.
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Conclusions on high-energy phenomena
In contrast to the thermal plasma, the non-equilibrium distributions ofCRs preserve the information about their injection and transportprocesses and provide thus a unique window of current and paststructure formation processes!
1 Cosmological hydrodynamical simulations are indispensable forunderstanding non-thermal processes in galaxy clusters→ illuminating the process of structure formation
2 Multi-messenger approach including radio synchrotron, hardX-ray IC, and HE γ-ray emission:
fundamental plasma physics: diffusive shock acceleration,large scale magnetic fields, and turbulencenature of dark mattergold sample of clusters for precision cosmology
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters
Introduction to dark matterIndirect dark matter searches
High-energy phenomena
Cosmological simulations with cosmic raysShocks and particle accelerationNon-thermal emission from clusters
Literature for the talk
Pinzke, Pfrommer, Bergström, Phys. Rev. Lett., 2009, 103, 181302, Gamma-raysfrom dark matter annihilations strongly constrain the substructure in halos
Pfrommer, 2008, MNRAS, 385, 1242 Simulating cosmic rays in clusters ofgalaxies – III. Non-thermal scaling relations and comparison to observations
Pfrommer, Enßlin, Springel, 2008, MNRAS, 385, 1211, Simulating cosmic rays inclusters of galaxies – II. A unified scheme for radio halos and relics withpredictions of the γ-ray emission
Pfrommer, Enßlin, Springel, Jubelgas, Dolag, 2007, MNRAS, 378, 385,Simulating cosmic rays in clusters of galaxies – I. Effects on theSunyaev-Zel’dovich effect and the X-ray emission
Pfrommer, Springel, Enßlin, Jubelgas, 2006, MNRAS, 367, 113,Detecting shock waves in cosmological smoothed particle hydrodynamicssimulations
Enßlin, Pfrommer, Springel, Jubelgas, 2007, A&A, 473, 41,Cosmic ray physics in calculations of cosmological structure formation
Jubelgas, Springel, Enßlin, Pfrommer, A&A, , 481, 33,Cosmic ray feedback in hydrodynamical simulations of galaxy formation
Christoph Pfrommer Dark Matter Searches in Galaxy Clusters