the role of the mti and hbi in the intracluster mediummctp/sciprgpgs/events/2010/plasma/... ·...
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The Role of the MTI and HBI in the Intracluster Medium
Ian ParrishChandra Fellow
UC Berkeley
Collaborators: Eliot Quataert, Mike McCourt, & Prateek Sharma
Physics of the Intracluster MediumAugust 23, 2010
1Tuesday, August 24, 2010
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2
4x106 M
BlackHole
Hydra A Cluster (Chandra)
T ~ 3-5 keV, n ~ 10-2-10-3 cm-3
Motivation50 kpc
large electron mean free path:
thermal conduction important & anisotropic
ρe ∼ 103
�T
3 keV
�1/2 �B
1 µG
�−1
km
λe ∼ 0.1�
T
3 keV
�2 � ne
0.03 cm−3
�−1kpc
2Tuesday, August 24, 2010
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Do we really have conduction?
P
T
ne
NGC4649(Churazov & Forman)
Either there is conduction or a vast cosmic conspiracy over 2 1/2 decades in density.
3Tuesday, August 24, 2010
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Structure in M87
2 Temperature fit to SW arm
(Werner, et al 2010: arxiv:1003.5334)Emission measure map of 1 keV plasma
Conduction is clearly efficient here.4Tuesday, August 24, 2010
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But...Cold Fronts
Requires suppression across front of ~100 to SpitzerSee John ZuHone’s Talks
(Markevitch & Vikhlinin 2007)
5Tuesday, August 24, 2010
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Presentation Outline
•Motivation•Beyond MHD in the Intracluster Medium The MTI in Cluster Outskirts.
The cooling flow problem & the HBI.Turbulence and Bimodality
•Filament Formation•Conclusions
6Tuesday, August 24, 2010
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Algorithm: MHD with Athena
∇ · B = 0
•Athena: Higher order Godunov Scheme.•Constrained transport for preserving divergence free constraint.•Anisotropic Heat flux (along B fields)
(Gardiner & Stone, 2008; Parrish & Stone, 2005)
∂ρ
∂t+∇ · (ρv) = 0,
(ρv)∂t
+∇ ·�ρvv +
�p +
B2
8π
�I − BB
4π
�= ρg,
∂E
∂t+∇ ·
�v
�E + p +
B2
8π
�− B(B · v)
4π
�= ρg · v −∇ · Q,
∂B
∂t−∇× (v ×B) = 0.
7Tuesday, August 24, 2010
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HBI (dT/dz > 0)MTI (dT/dz < 0)
a weakly magnetized plasma with anisotropic heat transportis always buoyantly unstable, independent of dT/dz!
Parrish & Stone 2005 Parrish & Quataert 2008
Buoyancy Instabilities in Magnetized Plasmas
8Tuesday, August 24, 2010
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Schwarzschild criterion ➔ clusters are stable
Radius (Rvir)
Entr
opy
Piffaretti et al. 2005
ds/dr > 0
Cluster Entropy Profiles
9Tuesday, August 24, 2010
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MTIr ≳ 100 kpc
average cluster temperature profile
HBIr ≲ 100 kpc
The Entire Cluster is Convectively Unstable!
Piffaretti et al. 2005
Radius (Rvir)
T/<
T>
~ 300 kpc
The MTI & HBI in Clusters
10Tuesday, August 24, 2010
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MTI in Clusters
11Tuesday, August 24, 2010
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MTI in Clusters
Temperature Profile becomes Isothermal
(Parrish, Stone, & Lem
aster, 2008)
3D Sims ofCluster Model
MTI growth time: ~ 800 Myr
12Tuesday, August 24, 2010
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MTI in Clusters
Magnetic Field Rearrangement:
Initially: 0.5 (tangled)Peak: ~0.68
�b · r�
B2f
B20
≈ 100
Heat conduction becomes more efficient
(Parrish, Stone, & Lemaster, 2008)
�b·r
�
Caveat: observed clusters are rarely isothermal:temperature gradient fixed by cosmological processes & infall.
13Tuesday, August 24, 2010
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MTI in Local Simulations
Can drive a strong dynamo, but only ~10 linear growth times in
outer parts of ICM.
14Tuesday, August 24, 2010
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MTI in Local Simulations with Turbulence
Stronger Turbulence
Consistent radial bias over isotropic, but small at large t.
See talk by Ruskowski on cosmological MTI
15Tuesday, August 24, 2010
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MTI Observed in Virgo?
Pfrommer & Dursi, Nature Physics 6 (2010)
Evidence for radially-oriented magnetic fields.16Tuesday, August 24, 2010
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Presentation Outline
•Motivation•Beyond MHD in the Intracluster Medium The MTI in Cluster Outskirts.The cooling flow problem & the HBI.Turbulence and Bimodality
•Filament Formation
17Tuesday, August 24, 2010
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HBI in Clusters: Abell 2199
T
ne
P
r (kpc)
Cluster Parameters:•Mass 3.8 x 1014 Msun
•rs ~ 390 kpc(Johnstone, et al 2002)•Hydrostatic Equilibrium•Thermal Equilibrium
Tangled Magnetic Fields
A = A0
�k
kpeak
�−α
B = ∇×A
HBI Growth Time:120 Myr(Parrish, Quataert, & Sharma 2009)
(Bogdanovic, et al 2009)
18Tuesday, August 24, 2010
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HBI in Clusters: Radial Fields
T (keV)
(t = 0) (t = 1.6 Gyr)
(t = 4.8 Gyr) (t = 9.5 Gyr)
Radial magnetic fields this slide only.
19Tuesday, August 24, 2010
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HBI in Clusters: A2199, Time EvolutionA
ngle
w.r.
t. ra
dial
T (
keV
)time (Myr) R (kpc)
• Magnetic geometry reorients to highly azimuthal• Conduction is reduced, fSp → 0.13.• HBI exacerbates cooling flow problem.
(Cooling catastrophe at 2.7 Gyr)20Tuesday, August 24, 2010
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Clusters and Entropy
Cavagnolo, Voit, D
onahue, et al (2009)
2 Populations!
• Hα• Radio•Blue Cores
• No Feedback Indicators
•More isothermal
K0 ≡T
n2/3e
21Tuesday, August 24, 2010
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Effect of Conduction on High Entropy Cores
with conduction
no conduction
K0 = 123, central cooling time = 9.3 Gyr (estimated)
22Tuesday, August 24, 2010
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Kolmogorov Turbulence:Drive on outer scale L with velocity V(L)
Eddies turn over on timescale
Turbulence in Clusters & CoolingSources of Turbulence:•Galaxy Wakes•Substructure•AGN•Mergers
X-Ray + Hα in A3627 Sun, Donahue, & Voit 2007
NASA/CXC/SOAR
ESO 137-001 leaves a wake
Galactic Wake Estimate•5 galaxies of mass within the central 200 kpc.•Outer turbulent scale of L ~ 40 kpc. •Turbulent Velocity: •Turbulent Energy:
1011 M⊙
δv ∼ 0.1cs
eturb � ρ(δv)3
L ≈ 7.5× 10−30 ergcm3 s
� ecool ∼ 10−27 ergcm3 s
teddy(L) = L/v(L)
v(λ) = v(L)�
λ
L
�1/3
23Tuesday, August 24, 2010
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The HBI and Turbulence
tHBI/teddy
Satu
rate
d M
agne
tic A
ngle
Local Simulations by McCourt
Two Limits:1) HBI efficient:
2) Turbulence wins:
tHBI < teddy
tHBI > teddy
fSp → 0
fSp → 13
Richardson Number (Ri)Ri = Fr−1/2
24Tuesday, August 24, 2010
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Turbulence and BimodalityFi
nal T
empe
ratu
re P
rofil
es Exact Same Initial Conditions
Turbulence of L = 40 kpc.
tHBI ≈ 100 Myrtcool ≈ 400 Myr
teddy ≈ 100− 450 Myr
Clear Bimodality:~25 km/s velocity difference•Stable ~isothermal profile•Cooling Catastrophe
Parrish, Quataert, & Sharma (2010)See also Ruszkowsi & Oh (2010)
25Tuesday, August 24, 2010
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Turbulence and Bimodality
Same δv ~ 115 km/s
L = 40 kpc L = 100 kpc
teddy ∼ L/δv
HBI shuts off conduction
Turbulence keeps conduction at fsp~1/3.
26Tuesday, August 24, 2010
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Turbulence and Bimodality
Snapshots at 7 Gyr
Stable Cooling Catastrophe
27Tuesday, August 24, 2010
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• Hα• Radio•Blue Cores
• No Feedback Indicators
•More isothermal
K0 ≡T
n2/3e
K0 = 11 Kf = 110
Turbulence and Entropy
Turbulence with 250 km/s
No Turbulence: HBI + cooling
•Conduction is a natural way to volumetrically raise entropy•Turbulence (energetically weak) can be a catalyst for changing the cool core/non-cool core state.
28Tuesday, August 24, 2010
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Conclusions on Bimodality
•The HBI can shut off conduction and precipitate a cooling catastrophe.•Conduction alone cannot stably heat a low-entropy, cool core cluster. These are mainly heated by feedback from a central AGN (bubbles, jets, etc). •Conduction can stably heat high entropy, fairly isothermal clusters...consistent with disturbed clusters being high entropy.•Small changes in turbulence naturally lead to a strong bimodality between these states.
K0 ≡T
n2/3e
29Tuesday, August 24, 2010
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Presentation Outline
•Motivation•Beyond MHD in the Intracluster Medium The MTI in Cluster Outskirts.
The cooling flow problem & the HBI.Turbulence and Bimodality•Filament Formation
30Tuesday, August 24, 2010
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Filament Observations in Perseus
NGC 1275: Observations (Fabian, et al)
31Tuesday, August 24, 2010
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Formation of Filaments with Anisotropic Conduction
Sharma, Parrish, & Quataert, arXiv:1003.5546, Accepted to ApJ
λF =�
Tκ(T )nenpΛ(T )
�1/2
Field’s LengthConduction Anisotropic
λF,� ≫ λF,⊥
• Cold, dense filaments aligned with magnetic field enhanced
by flux freezing.• Velocities of up to 100 km/s preferentially aligned with filaments.
32Tuesday, August 24, 2010