GH2005 Gas Dynamics in Clusters III Craig Sarazin Dept. of Astronomy University of Virginia A85 Chandra (X-ray) Cluster Merger Simulation

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

Merger with mass ratio of 3:1, offset merger (Ricker & Sarazin)

Cosmological simulation, temperature (Tittley)

Typical shock velocity 2000 km/s E (shock) ~ 3 x ergs Main heating mechanism of intracluster gas Merger Shocks Ricker & Sarazin

Merger Shocks (cont.) Although energetic, mainly weak shocks as cluster gas is already hot Mach numbers ℳ ≡ v s / c s ~ 1.5-2

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

Merger Boosts to L X & T X Ricker & Sarazin Mergers temporarily boost X-ray luminosity (factor of ≲ 10) Temperature (factor of ≲ 3) Are the most luminous, hottest clusters mainly mergers?

Merger Boosts (cont.) Randall et al. The most luminous, hottest clusters should mainly be mergers. Affects values of Ω M and σ 8 from luminous clusters.

Merger Boosts to L X & T X Boost → Ω M underestimated by ~20% σ 8 overestimated by ~20%

Merger Boosts of SZ Effect Mergers compress, heat gas, increase pressure → increase SZ effect r SZ = characteristic radius

SZ Merger Boosts (Cont.) y 0 or Y y0y0 Y

Merger Boosts (cont.) (Meneghetti et al., Randall et al.) Lensing studies of masses of most luminous, hottest clusters confirm merger boosts L X & T x Mergers boost S-Z effect (Wik et al.) Mergers also appear to boost probability of strong lensing Smith et al.

Merger simulations → turbulence in post merger shock regions of clusters E turb ≈ 20% E therm, decays following merger (Ricker & Sarazin) Explains radio halos in merging clusters? Astro-E2 should detect turbulence in merging, radio halo clusters Turbulence and Mergers

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

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  

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  

Chandra: “ Cold Fronts” in Mergers Merger shocks? No: Dense gas is cooler, lower entropy, same pressure as lower density gas Abell 2142 Markevitch et al.

Contact discontinuity, cool cluster cores plowing through hot shocked gas Abell 3667 Vikhlinin et al. Cold Fronts (cont.)

Markevitch et al. 1E Abell 2034Abell 85 South Kempner et al. 2002,2003

Cold Front with Merger Bow Shock 1E Markevitch et al.

Cool Trails Behind Cold Fronts Cold fronts with cool trails behind (due to ram pressure) Abell 1644 (Reiprich et al.) Image XMM-Newton Hardness Simulation Tittley

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

Give merger Mach number ℳ Rankine-Hugoniot shock jump conditions r 2 / r 1 = (γ + 1) ℳ 2 /[(γ - 1) ℳ 2 + 2] P 2 /P 1 = [2γℳ 2 - (γ - 1)]/(γ + 1) g = 5/3 Merger Kinematics

Cold Front with Merger Bow Shock 1E Markevitch et al.

Give merger Mach number ℳ Rankine-Hugoniot shock jump conditions r 2 / r 1 = (γ + 1) ℳ 2 /[(γ - 1) ℳ 2 + 2] P 2 /P 1 = [2γℳ 2 - (γ - 1)]/(γ + 1) g = 5/3 Merger Kinematics

Give merger Mach number ℳ Rankine-Hugoniot shock jump conditions Mach cone angle Merger Kinematics

Cold Front with Merger Bow Shock 1E Markevitch et al.

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

Merger Kinematic Diagnostics

Give merger Mach number ℳ Rankine-Hugoniot shock jump conditions Mach cone angle Stagnation condition at cold front Merger Kinematics

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

Shock stand-off distance (Sarazin 2002)

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 Find ℳ ≈ 1.5-2, shock velocity ≈ 2000 km/s Merger Kinematics

Merger Kinematics – Abell 85 ℳ = 1.4, v = 2150 km/s D = 1.23 Mpc, q v = 71 o, q d = 144 o, f v = -36 o, f d = 194 o, y = 52 o Shock velocity = expected from infall → Shocks effectively thermalize kinetic energy Kempner et al

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.