Magnetohydrodynamics of Cloud Collisions in a Multi-phase Interstellar Medium

Abstract

We extend previous studies of the physics of interstellar cloud collisions by beginning investigation of the role of magnetic fields through 2D magnetohydrodynamic (MHD) numerical simulations. We study head-on collisions between equal mass, mildly supersonic diffuse clouds. We include a moderate magnetic field and two limiting field geometries, with the field lines parallel (aligned) and perpendicular (transverse) to the colliding cloud motion. We explore both adiabatic and radiative cases, as well as symmetric and asymmetric ones. We also compute collisions between clouds evolved through prior motion in the intercloud medium and compare with unevolved cases. We find that: In the (i) aligned case, adiabatic collisions, like their HD counterparts, are very disruptive, independent of the cloud symmetry. However, when radiative processes are taken into account, partial coalescence takes place even in the asymmetric case, unlike the HD calculations. In the (ii) transverse case, collisions between initially adjacent unevolved clouds are almost unaffected by magnetic fields. However, the interaction with the magnetized intercloud gas during the pre-collision evolution produces a region of very high magnetic energy in front of the cloud. In collisions between evolved clouds with transverse field geometry, this region acts like a ``bumper'', preventing direct contact between the clouds, and eventually reverses their motion. The ``elasticity'', defined as the ratio of the final to the initial kinetic energy of each cloud, is about 0.5-0.6 in the cases we considered. This behavior is found both in adiabatic and radiative cases.

40 pages in AAS LaTeX v4.0, 13 figures (in degraded jpeg format). Full resolution images as well as mpeg animations are available at http://www.msi.umn.edu:80/Projects/twj/mhd-cc/ . Accepted for publication in The Astrophysical Journal

References in corpus (5)

• A Divergence-Free Upwind Code for Multidimensional Magnetohydrodynamic Flows
• The MHD Kelvin-Helmholtz Instability II: The Roles of Weak and Oblique Fields in Planar Flows
• The survival of interstellar clouds against Kelvin-Helmholtz instabilities
• Hydrodynamics of Cloud Collisions in 2D: The Fate of Clouds in a Multi-phase Medium
• Energy Dissipation in Interstellar Cloud Collisions

Cited by in corpus (15)

• The Role of Stellar Feedback and Dark Matter in the Evolution of Dwarf Galaxies
• Formation of Massive Molecular Cloud Cores by Cloud-cloud Collision
• Magnetized Gas Clouds can Survive Acceleration by a Hot Wind
• Interaction of a cold cloud with a hot wind: the regimes of cloud growth and destruction and the impact of magnetic fields
• Magnetic Fields in Stellar Jets
• Filament formation in wind-cloud interactions. II. Clouds with turbulent density, velocity, and magnetic fields
• Enhanced Cloud Disruption by Magnetic Field Interaction
• The Launching of Cold Clouds by Galaxy Outflows III: The Influence of Magnetic Fields
• Constrained-Transport Magnetohydrodynamics with Adaptive-Mesh-Refinement in CHARM
• On the Exchange of Kinetic and Magnetic Energy Between Clouds and the Interstellar Medium
• MHD Shock-Clump Evolution with Self-Contained Magnetic Fields
• Shock-triggered formation of magnetically-dominated clouds. II. Weak shock-cloud interaction in three dimensions
• Existence and Uniqueness of Strong Solutions for a Compressible Multiphase Navier-Stokes Miscible Fluid-Flow Problem in Dimension n = 1
• The CARMA-NRO Orion Survey: Filament Formation via Collision-Induced Magnetic Reconnection -- The Stick in Orion A
• What regulates the velocity distribution of interstellar clouds?