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 A Panel of Simulation Images?

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 Introduction Outline 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.

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

Previous Results: Hydrodynamic Clumps

Density log plot at 2τ cc (top) and 6τ cc (bottom). Left: β = 4. Right: β = 256. Field line plot at 2τ cc (top) and 6τ cc (bottom). Left: β = 4. Right: β = 256. 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. Jones, T.W., Ryu, Dongsu, Tregillis, I.L ApJ, 473, 365 Previous Results: Clumps with a Uniform External Magnetic Field

Density log plot at 2τ cc (top) and 6τ cc (bottom). Left: β = 4. Right: β = 256. Field line plot at 2τ cc (top) and 6τ cc (bottom). Left: β = 4. Right: β = 256. 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. Jones, T.W., Ryu, Dongsu, Tregillis, I.L ApJ, 473, 365 Previous Results: Clumps with a Uniform External Magnetic Field

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) Previous Results: Clumps with External Magnetic Field and Radiative Cooling

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

Methodology A Panel of Image of the Day? 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.

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.

Table of Runs Field Strength (Magnetic β) Field StructureOrientation (Relative to Shock Direction) Power Spectral index BX10.5 External, Uniform ‖ - BX28 External, Uniform ‖ - BY10.5 External, Uniform ┴- BY28 External, Uniform ┴- BCTP0.1 Contained, Toroidal Only ┴- BCTA0.1 Contained, Toroidal Only ‖ - BCPP0.1 Contained, Poloidal Only ┴- BCPA0.1 Contained, Poloidal Only ‖ - BCRF10.1 Contained, Random -0 BCRF21 Contained, Random -0 BCRK10.1 Contained, Random - -11/3 BCRK21 Contained, Random - -11/3 Clump Density Contrast χ = 100 Ambient Density n amb = 1 cc Ambient Temperature T amb = 10 K Clump Radius R = 150 AU Shock Mach M = 10 Simulation Parameters 4

MHD clumps with External Magnetic Field

MHD clumps with Contained Magnetic Field Case BCTP

MHD clumps with Contained Magnetic Field Case BCTA

MHD clumps with Contained Magnetic Field Case BCPP

MHD clumps with Contained Magnetic Field Case BCPA

MHD clumps with Contained Magnetic Field 50% Cut Movies

MHD clumps with Contained Magnetic Field Special Case: Toroidal Combined with Poloidal

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

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

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

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

MHD clumps with Contained Magnetic Field Case BRF1, BRF2

MHD clumps with Contained Magnetic Field Case BRK1,BRK2

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

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

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

MHD clumps with Contained Magnetic Field Mixing Ratio Line Plots

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

MHD clumps with Contained Magnetic Field Vorticity Line Plots

MHD clumps with Contained Magnetic Field Power Spectrum Line Plots

MHD clumps with Contained Magnetic Field Discussion and Quantitative Result

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