Shule Li, Adam Frank, Eric Blackman

1. Clumps With External Magnetic Fields, Their Interaction With Shocks, and the Effect of Magnetic Thermal Conduction Shule Li, Adam Frank, Eric Blackman University of Rochester, Department of Physics and Astronomy. Rochester, New York 14627 A Panel of Simulation Images?

2. Introduction Problems involving magnetized clouds and clumps, especially their interaction with shocks are common in astrophysical environments and have been a topic of research in the past decade. The magnetic field structure, whether aligned with the shock or perpendicular to the shock, can have profound influence on the shocked behavior and evolution of the clump. Most previous numerical studies have focused on the scenario where the shocked clump is immersed in a uniform background. In this presentation we take one step further to assume a more realistic scenario where the clumps have the tangled magnetic field residing inside. These clumps can be formed when winds blowing through a magnetized clumpy background medium detach the medium along with the field lines. We will show that the contained magnetic field can have great influence on the post-shock clump evolution. Some of them may lead to observational evidence of the magnetic field structure in the interstellar medium. Outline 1. Previous works on MHD shocked clump simulations 2. Description of the problem 3. Goals and methods of the current study 4. Table of Runs 5. Simulations of MHD clumps with external magnetic field 6. Simulations of MHD clumps with contained magnetic field 7. Discussion and conclusion

3. Problem Description Meaningful Quantities wind Density Contrast: Sonic Mach number: ambient clump Alfvenic Mach number: Magnetic Beta: Clump crushing time:

4. Previous Results: Hydrodynamic Clumps

5. Previous Results: Clumps with a Uniform External Magnetic Field When the external field is parallel to the shock propagation direction: No significant difference in terms of density evolution even for β = 1. The criterion for the magnetic field removing K-H instabilities at the clump boundaries is: β < 1 along the boundary. The criterion for the magnetic field to stabilize R-T instabilities is roughly: β < χ/M. But there is no place that the magnetic field becomes energetically dominant; that is, almost everywhere β >> 1. Magnetic fields stretched over the top of the clump can have a significant stabilizing influence that improves the flow coherence. Density log plot at 2τcc (top) and 6τcc (bottom). Left: β = 4. Right: β = 256. Field line plot at 2τcc (top) and 6τcc (bottom). Left: β = 4. Right: β = 256. Jones, T.W., Ryu, Dongsu, Tregillis, I.L. 1996 ApJ, 473, 365

6. Previous Results: Clumps with a Uniform External Magnetic Field When the external field is perpendicular with the shock propagation direction: The magnetic field is stretched and wrapped around the clump, which effectively confines the clump and prevents its fragmentation, even for moderately strong field β = 4. The clump embedded in the stretched field is compressed, but then, because of the strong confining effect of the field develops a streamlined profile and is not strongly eroded. The magnetic pressure at the nose of the clump increases drastically, which acts as a shock absorber. At later stage, the stretched field around the clump edge has β < 1 even for moderately strong initial field condition. This protects the clump from further disruption. Density log plot at 2τcc (top) and 6τcc (bottom). Left: β = 4. Right: β = 256. Field line plot at 2τcc (top) and 6τcc (bottom). Left: β = 4. Right: β = 256. Jones, T.W., Ryu, Dongsu, Tregillis, I.L. 1996 ApJ, 473, 365

7. Previous Results: Clumps with External Magnetic Field and Radiative Cooling With radiative cooling added to the simulation, people found that the shocked behavior of clumps can change drastically comparing to the addiabatic cases. Bow shock and transmitted shock have different cooling time. This fact divides the parameter space into 4 different regimes. Thin fragments which are dense and cold are developed after shock. The boundary flows are streamlined when the bow shock cools efficiently. Balk of cooled clump material tightly bounded by the bow shock is formed when transmitted shock cools efficiently. The clump behavior depends heavily on actually cooling routine implemented in the simulation Code. Fragile et al (2005 ApJ 619, 327)

8. Previous Results: 3D Simulations on Shocked Clumps Min-Su Shin, James M. Stone, Gregory F. Snyder, 2008 ApJ, 680, 336 3D density contour (left) and magnetic pressure (right) for weak aligned field, perpendicular field, and oblique shock cases, at 4τcc. 3D density contour at various clump crushing time for weak and strong aligned field.

9. Methodology AstroBEAR is a parallelized hydrodynamic/MHD simulation code suitable for a variety of astrophysical problems. Derived from the BearCLAW package written by Sorin Mitran, AstroBEAR is designed for 2D and 3D adaptive mesh refinement (AMR) simulations. The 2.0 version of the code shows good scaling in various tests up to 2000 processors. Users write their own project modules by specifying initial conditions and continual processes (such as an inflow condition). In addition, AstroBEAR comes with a number of multiphysical processes such as self gravity and thermal conduction, pre-built physical phenomena such as clumps and winds that can be loaded into a user module. A Panel of Image of the Day?

10. Methodology MHD Equations with Radiative cooling is implemented via operator splitting, with several built-in cooling tables. In the presented simulations, we use Dalgano-Mcray cooling table.

11. Table of Runs Simulation Parameters Ambient Density namb = 1 cc -1 Ambient Temperature Tamb = 10 K 4 Clump Density Contrast χ = 100 Clump Radius R = 150 AU Shock Mach M = 10

13. MHD clumps with External Magnetic Field http://www.pas.rochester.edu/~smurugan/

14. MHD clumps with Contained Magnetic Field Case BCTP http://www.pas.rochester.edu/~shuleli/HedlaMovie/torzvr.gif

15. MHD clumps with Contained Magnetic Field Case BCTA http://www.pas.rochester.edu/~shuleli/HedlaMovie/torxvr.gif

16. MHD clumps with Contained Magnetic Field Case BCPP http://www.pas.rochester.edu/~shuleli/HedlaMovie/polzvr.gif

17. MHD clumps with Contained Magnetic Field Case BCPA http://www.pas.rochester.edu/~shuleli/HedlaMovie/polxvr.gif

18. MHD clumps with Contained Magnetic Field 50% Cut Movies http://www.pas.rochester.edu/~smurugan/

19. MHD clumps with Contained Magnetic Field Special Case: Toroidal Combined with Poloidal http://www.pas.rochester.edu/~shuleli/HedlaMovie/tp1vr.gif http://www.pas.rochester.edu/~shuleli/HedlaMovie/tp2vr.gif

20. MHD clumps with Contained Magnetic Field Discussion and Conclusion 1: Ordered Field

21. MHD clumps with Contained Magnetic Field Discussion and Conclusion 1: Ordered Field

22. MHD clumps with Contained Magnetic Field Discussion and Conclusion 1: Ordered Field

23. MHD clumps with Contained Magnetic Field Discussion and Conclusion 1: Ordered Field

24. MHD clumps with Contained Magnetic Field Case BRF1, BRF2

25. MHD clumps with Contained Magnetic Field Case BRK1,BRK2 http://www.pas.rochester.edu/~shuleli/HedlaMovie/kolsvr.gif

26. MHD clumps with Contained Magnetic Field Magnetic Energy Line Plots: Ordered Field

27. MHD clumps with Contained Magnetic Field Magnetic Energy Line Plots: Random Field

28. MHD clumps with Contained Magnetic Field Kinetic and Thermal Energy Line Plots

29. MHD clumps with Contained Magnetic Field Mixing Ratio Line Plots

30. MHD clumps with Contained Magnetic Field Mixing Ratio Line Plots: Different Beta

31. MHD clumps with Contained Magnetic Field Vorticity Line Plots

32. MHD clumps with Contained Magnetic Field Power Spectrum Line Plots

33. MHD clumps with Contained Magnetic Field Discussion and Quantitative Result

34. MHD clumps with Contained Magnetic Field Conclusion 2: From Line Plots