GH2005 Gas Dynamics in Clusters III

1. GH2005Gas Dynamics in Clusters III Craig Sarazin Dept. of Astronomy University of Virginia Cluster Merger Simulation A85 Chandra (X-ray)

2. Thermal Effects of Mergers • 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

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

4. Cosmological simulation, temperature (Tittley)

5. Merger Shocks • Typical shock velocity 2000 km/s • E (shock) ~ 3 x 1063 ergs • Main heating mechanism of intracluster gas Ricker & Sarazin

6. Merger Shocks (cont.) • Although energetic, mainly weak shocks as cluster gas is already hot • Mach numbers ℳ ≡ vs / cs ~ 1.5-2

7. 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

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

9. Merger Boosts (cont.) The most luminous, hottest clusters should mainly be mergers. Affects values of ΩM and σ8 from luminous clusters. Randall et al.

10. Merger Boosts to LX & TX Boost → ΩM underestimated by ~20% σ8 overestimated by ~20%

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

12. SZ Merger Boosts (Cont.) y0 y0 or Y Y

13. Merger Boosts (cont.) 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. (Meneghetti et al., Randall et al.)

14. Turbulence and Mergers • 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

15. Astro-E2 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

16. Mergers Disrupt Cool Cores 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 Ricker & Sarazin

17. Cool Cores in Mergers 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 Ricker & Sarazin

18. 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.

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

20. Cold Fronts (cont.) 1E0657-56 Abell 2034 Abell 85 South Markevitch et al. Kempner et al. 2002,2003

21. Cold Front with Merger Bow Shock Markevitch et al. 1E0657-56

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

23. 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

24. Merger Kinematics • 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

25. Cold Front with Merger Bow Shock Markevitch et al. 1E0657-56

26. Merger Kinematics • 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

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

28. Cold Front with Merger Bow Shock Markevitch et al. 1E0657-56

29. 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

30. Merger Kinematic Diagnostics

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

32. 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

33. Shock stand-off distance (Sarazin 2002)

34. 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 • Find ℳ ≈ 1.5-2, shock velocity ≈ 2000 km/s

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

36. Transport Processes – Thermal Conduction Ettori & Fabian; Vikhlinin 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?