gh2005 gas dynamics in clusters iii
DESCRIPTION
GH2005 Gas Dynamics in Clusters III. Craig Sarazin Dept. of Astronomy University of Virginia. Cluster Merger Simulation. A85 Chandra (X-ray). Thermal Effects of Mergers. Heat and compress ICM Increase entropy of gas Boost X-ray luminosity, temperature, SZ effect Mix gas - PowerPoint PPT PresentationTRANSCRIPT
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GH2005Gas Dynamics in Clusters III
Craig SarazinDept. of Astronomy
University of Virginia
A85 Chandra (X-ray)Cluster Merger
Simulation
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• Heat and compress ICM• Increase entropy of gas• Boost X-ray luminosity, temperature, SZ
effect• Mix gas• Disrupt cool cores• Produce turbulence• Provide diagnostics of merger kinematics
Thermal Effects of Mergers
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Merger with mass ratio of 3:1, offset merger (Ricker & Sarazin)
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Cosmological simulation, temperature (Tittley)
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• Typical shock velocity 2000 km/s
• E (shock) ~ 3 x 1063 ergs
• Main heating mechanism of intracluster gas
Merger Shocks
Ricker & Sarazin
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Merger Shocks (cont.)• Although energetic, mainly weak shocks as
cluster gas is already hot
• Mach numbers ℳ ≡ vs / cs ~ 1.5-2
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Merger Shocks (cont.)
Shocks are hard to see in X-rays in clusters• Shocks → more heating than compression• Weak shocks → small compressions, not very bright in X-
rays• Projection effects
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Merger Boosts to LX & TX
Ricker & Sarazin
•Mergers temporarily boost
•X-ray luminosity (factor of ≲ 10)
•Temperature (factor of ≲ 3)
•Are the most luminous, hottest clusters mainly mergers?
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Merger Boosts (cont.)
Randall et al.
The most luminous, hottest clusters should mainly be mergers. Affects values of ΩM and σ8 from luminous clusters.
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Merger Boosts to LX & TX
Boost → ΩM underestimated by ~20%
σ8 overestimated by ~20%
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Merger Boosts of SZ EffectMergers compress, heat gas, increase pressure
→ increase SZ effect
rSZ = characteristic radius
Pdldlncm
kTy eT
e
2
AAyPdVydAY area large
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SZ Merger Boosts (Cont.)y
0 or
Y
y0
Y
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Merger Boosts (cont.)
(Meneghetti et al., Randall et al.)
Lensing studies of masses of most luminous, hottest clusters confirm merger boosts LX & Tx
Mergers boost S-Z effect (Wik et al.)
Mergers also appear to boost probability of strong lensing
Smith et al.
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•Merger simulations → turbulence in post merger shock regions of clusters
•Eturb ≈ 20% Etherm , decays following merger (Ricker & Sarazin)
•Explains radio halos in merging clusters?
•Astro-E2 should detect turbulence in merging, radio halo clusters
Turbulence and Mergers
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•High spectral resolution, nondispersive X-ray spectra
•Directly measure Doppler shifts in X-rays due to gas motions in clusters
•Line widths → turbulence in cluster
•Launch in summer 2005
Astro-E2 and Mergers
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Observed anticorrelation between mergers and cool cores
Not due to shocks – density gradient too big
Mainly due to ram pressure, changes in potential, instabilities, & mixing
Mergers Disrupt Cool Cores
Ricker
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Cool cores → high density gas at bottom of deep potential well
Cool cores can survive for some time in mergers
Almost like a solid object moving through cluster
High density → prominent in X-ray images
Sharp front edge → very prominent in Chandra images
Cool Cores in Mergers
Ricker
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Chandra: “Cold Fronts” in Mergers
Merger shocks?
No: Dense gas is cooler, lower entropy, same pressure as lower density gas
Abell 2142Markevitch et
al.
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Contact discontinuity, cool cluster cores plowing through hot shocked gas
Abell 3667
Vikhlinin et al.
Cold Fronts (cont.)
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Cold Fronts (cont.)
Markevitch et al.
1E0657-56 Abell 2034 Abell 85 South
Kempner et al. 2002,2003
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Cold Front with Merger Bow Shock
1E0657-56
Markevitch et al.
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Cool Trails Behind Cold Fronts
Cold fronts with cool trails behind (due to ram pressure)
Abell 1644 (Reiprich et al.)
Image XMM-Newton HardnessSimulation
Tittley
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Give merger Mach number ℳ• Rankine-Hugoniot shock jump conditions• Mach cone angle• Stagnation condition at cold front• Stand-off distance of bow shock from cold
front
Merger Kinematics
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Give merger Mach number ℳ• Rankine-Hugoniot shock jump conditions
r2/ r1 = (γ + 1) ℳ 2 /[(γ - 1) ℳ 2 + 2]
P2/P1 = [2γℳ 2 - (γ - 1)]/(γ + 1)g = 5/3
Merger Kinematics
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Cold Front with Merger Bow Shock
1E0657-56
Markevitch et al.
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Give merger Mach number ℳ• Rankine-Hugoniot shock jump conditions
r2/ r1 = (γ + 1) ℳ 2 /[(γ - 1) ℳ 2 + 2]
P2/P1 = [2γℳ 2 - (γ - 1)]/(γ + 1)g = 5/3
Merger Kinematics
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Give merger Mach number ℳ• Rankine-Hugoniot shock jump conditions• Mach cone angle
Merger Kinematics
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Cold Front with Merger Bow Shock
1E0657-56
Markevitch et al.
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Give merger Mach number ℳ• Rankine-Hugoniot shock jump conditions• Mach cone angle• Stagnation condition at cold front• Stand-off distance of bow shock from cold
front
Merger Kinematics
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Merger Kinematic Diagnostics
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Give merger Mach number ℳ• Rankine-Hugoniot shock jump conditions• Mach cone angle• Stagnation condition at cold front
Merger Kinematics
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Give merger Mach number ℳ• Rankine-Hugoniot shock jump conditions• Mach cone angle• Stagnation condition at cold front• Stand-off distance of bow shock from cold
front
Merger Kinematics
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Shock stand-off distance (Sarazin 2002)
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Give merger Mach number ℳ• Rankine-Hugoniot shock jump conditions• Mach cone angle• Stagnation condition at cold front• Stand-off distance of bow shock from cold
frontFind ℳ ≈ 1.5-2, shock velocity ≈ 2000
km/s
Merger Kinematics
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Merger Kinematics – Abell 85
ℳ = 1.4, v = 2150 km/sD = 1.23 Mpc, qv = 71o, qd = 144o, fv = -36o, fd = 194o, y = 52oShock velocity = expected from infall →
Shocks effectively thermalize kinetic energy
Kempner et al
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• Temperature changes by 5x in ≲ 5 kpc < mfp
• Thermal conduction suppressed by ~ 100 x
• Kelvin-Helmholtz instabilities suppressed
• Due to transverse or tangled magnetic field?Is conduction generally suppressed in clusters?
Transport Processes – Thermal Conduction
Ettori & Fabian; Vikhlinin et al.