MHD Simulations of the ISM: The Importance of the Galactic Magnetic Field on the ISM “Phases”
نویسندگان
چکیده
We have carried out 1.25 pc resolution MHD simulations of the ISM, on a Cartesian grid of 0 ≤ (x, y) ≤ 1 kpc size in the galactic plane and −10 ≤ z ≤ 10 kpc into the halo, thus being able to fully trace the time-dependent evolution of the galactic fountain. The simulations show that large scale gas streams emerge, driven by SN explosions, which are responsible for the formation and destruction of shocked compressed layers. The shocked gas can have densities as high as 800 cm and lifetimes up to 15 Myr. The cold gas is distributed into filaments which tend to show a preferred orientation due to the anisotropy of the flow induced by the galactic magnetic field. Ram pressure dominates the flow in the unstable branch 10 <T≤ 10 K, while for T≤ 100 K (stable branch) magnetic pressure takes over. Near supernovae thermal and ram pressures determine the dynamics of the flow. Up to 80% of the mass in the disk is concentrated in the thermally unstable regime 10 <T≤ 10 K with ∼ 30% of the disk mass enclosed in the T≤ 10 K gas. The hot gas in contrast is controlled by the thermal pressure, since magnetic field lines are swept towards the dense compressed walls.
منابع مشابه
Global galactic dynamo driven by cosmic-rays and exploding magnetized stars
We report first results of first global galactic-scale CR-MHD simulations of cosmicray-driven dynamo. We investigate the dynamics of magnetized interstellar medium (ISM), which is dynamically coupled with the cosmic-ray (CR) gas. We assume that exploding stars deposit small-scale, randomly oriented, dipolar magnetic fields into the differentially rotating ISM, together with a portion of cosmic ...
متن کاملThree-dimensional Simulations of Magnetized Superbubbles: New Insights into the Importance of Mhd Effects on Observed Quantities
We present three-dimensional magnetohydrodynamic (MHD) simulations of superbubbles, to study the importance of MHD effects in the interpretation of images from recent surveys of the Galactic plane. These simulations focus mainly on atmospheres defined by an exponential density distribution and the Dickey & Lockman (1990) density distribution. In each case, the magnetic field is parallel to the ...
متن کاملGeneration of Alfvén Waves by Small-Scale Magnetic Reconnection in Solar Spicules
Alfvén waves dissipation is an extensively studied mechanism for the coronal heating problem. These waves can be generated by magnetic reconnection and propagated along the reconnected field lines. Here, we study the generation of Alfvén waves at the presence of both steady flow and sheared magnetic field in the longitudinally density stratified of solar spicules. The initial flow is assumed to...
متن کاملOverview of the ISM Phases: Evolution of Large and Small Scale Structures in 3D high resolution HD and MHD simulations
We review recent 3D high resolution numerical HD and MHD studies of a multi-component and multi-phase ISM. The computational grid was chosen large enough in the disk to represent typical ISM gas patterns, and in the halo to include the full extent of the Galactic fountain. The evolution of the ISM is driven by supernovae of all types and followed for 400 Myrs, long enough to get rid of memory e...
متن کاملTransport of Positrons in the Interstellar Medium
This work investigates some aspects of the transport of low-energy e (Ek . 1 MeV) in the interstellar medium (ISM). We consider resonance interactions with magnetohydrodynamic (MHD) waves above the resonance threshold. Below the threshold, collisions take over and deflect e in their motion parallel to magnetic-field lines. Using Monte-Carlo simulations, we model the propagation and energy losse...
متن کامل