scholarly journals Insights into the physics when modelling cold gas clouds in a hot plasma

2019 ◽  
Vol 490 (1) ◽  
pp. L52-L56
Author(s):  
Bastian Sander ◽  
Gerhard Hensler
Keyword(s):  
Adaptive Mesh Refinement ◽  
Adaptive Mesh ◽  
Careful Consideration ◽  
Necessary Condition ◽  
Interstellar Clouds ◽  
Hot Plasma ◽  
Magnetic Dipole Field ◽  
Set Up ◽  
Self Gravity ◽  
Cold Gas

ABSTRACT This paper aims at studying the reliability of a few frequently raised, but not proven, arguments for the modelling of cold gas clouds embedded in or moving through a hot plasma and at sensitizing modellers to a more careful consideration of unavoidable acting physical processes and their relevance. At first, by numerical simulations we demonstrate the growing effect of self-gravity on interstellar clouds and, by this, moreover argue against their initial set-up as homogeneous. We apply the adaptive-mesh refinement code flash with extensions to metal-dependent radiative cooling and external heating of the gas, self-gravity, mass diffusion, and semi-analytic dissociation of molecules, and ionization of atoms. We show that the criterion of Jeans mass or Bonnor–Ebert mass, respectively, provides only a sufficient but not a necessary condition for self-gravity to be effective, because even low-mass clouds are affected on reasonable dynamical time-scales. The second part of this paper is dedicated to analytically study the reduction of heat conduction by a magnetic dipole field. We demonstrate that in this configuration, the effective heat flow, i.e. integrated over the cloud surface, is suppressed by only 32 per cent by magnetic fields in energy equipartition and still insignificantly for even higher field strengths.

scholarly journals How to Simulate the Universe in a Computer

2005 ◽  
Vol 22 (3) ◽  
pp. 184-189 ◽  
Author(s):  
Alexander Knebe
Keyword(s):  
Adaptive Mesh Refinement ◽  
Initial Conditions ◽  
Adaptive Mesh ◽  
General Idea ◽  
Short Introduction ◽  
Set Up ◽  
Self Gravity ◽  
Tree Codes ◽  
The Universe ◽  
Broad Overview

AbstractIn this contribution a broad overview of the methodologies of cosmological N-body simulations and a short introduction explaining the general idea behind such simulations is presented. After explaining how to set up the initial conditions using a set of N particles two (diverse) techniques are presented for evolving these particles forward in time under the influence of their self-gravity. One technique (tree codes) is solely based upon a sophistication of the direct particle–particle summation whereas the other method relies on the continuous (de-)construction of arbitrarily shaped grids and is realized in adaptive mesh refinement codes.

scholarly journals Turbulent structure and star formation in a stratified, supernova-driven, interstellar medium

2006 ◽  
Vol 2 (S237) ◽  
pp. 358-362
Author(s):  
M. K. Ryan Joung ◽  
Mordecai-Mark Mac Low
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Adaptive Mesh Refinement ◽  
Formation Rate ◽  
Three Dimensional ◽  
Adaptive Mesh ◽  
Mass Function ◽  
Initial Mass Function ◽  
Interstellar Turbulence ◽  
Self Gravity

AbstractWe report on a study of interstellar turbulence driven by both correlated and isolated supernova explosions. We use three-dimensional hydrodynamic models of a vertically stratified interstellar medium run with the adaptive mesh refinement code Flash at a maximum resolution of 2 pc, with a grid size of 0.5 × 0.5 × 10 kpc. Cold dense clouds form even in the absence of self-gravity due to the collective action of thermal instability and supersonic turbulence. Studying these clouds, we show that it can be misleading to predict physical properties such as the star formation rate or the stellar initial mass function using numerical simulations that do not include self-gravity of the gas. Even if all the gas in turbulently Jeans unstable regions in our simulation is assumed to collapse and form stars in local freefall times, the resulting total collapse rate is significantly lower than the value consistent with the input supernova rate. The amount of mass available for collapse depends on scale, suggesting a simple translation from the density PDF to the stellar IMF may be questionable. Even though the supernova-driven turbulence does produce compressed clouds, it also opposes global collapse. The net effect of supernova-driven turbulence is to inhibit star formation globally by decreasing the amount of mass unstable to gravitational collapse.

scholarly journals Global simulations of galactic discs: violent feedback from clustered supernovae during bursts of star formation

2019 ◽  
Vol 492 (1) ◽  
pp. 79-95 ◽  
Author(s):  
Davide Martizzi
Keyword(s):  
Adaptive Mesh Refinement ◽  
Gravitational Instability ◽  
Adaptive Mesh ◽  
Dark Matter Halo ◽  
Time Variability ◽  
Mass Loading ◽  
Star Forming ◽  
Galactic Winds ◽  
Self Gravity ◽  
Supernova Feedback

ABSTRACT A suite of idealized, global, gravitationally unstable, star-forming galactic disc simulations with 2 pc spatial resolution, performed with the adaptive mesh refinement code ramses, is used in this paper to predict the emergent effects of supernova feedback. The simulations include a simplified prescription for the formation of single stellar populations of mass $\sim 100 \, {\rm M}_{\odot }$, radiative cooling, photoelectric heating, an external gravitational potential for a dark matter halo and an old stellar disc, self-gravity, and a novel implementation of supernova feedback. The results of these simulations show that gravitationally unstable discs can generate violent supersonic winds with mass-loading factors η ≳ 10, followed by a galactic fountain phase. These violent winds are generated by highly clustered supernovae exploding in dense environments created by gravitational instability, and they are not produced in simulation without self-gravity. The violent winds significantly perturb the vertical structure of the disc, which is later re-established during the galactic fountain phase. Gas resettles into a quasi-steady, highly turbulent disc with volume-weighted velocity dispersion $\sigma \gt 50 \, {\rm km\, s}^{-1}$. The new configuration drives weaker galactic winds with a mass-loading factor η ≤ 0.1. The whole cycle takes place in ≤10 dynamical times. Such high time variability needs to be taken into account when interpreting observations of galactic winds from starburst and post-starburst galaxies.

The NEMO (Nucleus for European Modelling of the Ocean) numerical ocean platform

2020 ◽  
Author(s):  
Guillaume Samson ◽  
Claire Levy ◽  
Nemo System Team
Keyword(s):  
Adaptive Mesh Refinement ◽  
State Of The Art ◽  
Adaptive Mesh ◽  
Ocean Model ◽  
Ocean Dynamics ◽  
Ice Shelves ◽  
Model Code ◽  
Set Up ◽  
Climate Studies

<p>The Nucleus for European Modelling of the Ocean (NEMO) is a state-of-the art modelling platform for oceanographic research, operational oceanography, sesonnal forecasts and climate studies. NEMO includes three major components; the blue ocean (dynamics), the white ocean (sea-ice), the green ocean (ocean biogeochemistry). It also allows coupling through interfaces with atmosphere (through OASIS software), waves, ice-shelves, so as nesting through the adaptive mesh refinement software AGRIF. Some reference configurations and test cases allowing to explore, to set-up and to validate the applications, and a set of tools to use the platform are also available to the community. The whole platform and its documentation are available under free licence.</p><p>The evolution and reliability of NEMO are organised and controlled by a European Consortium between CMCC (Italy), CNRS (France), MOI France), NOC (UK), UKMO (UK).</p><p>Consortium members agree on long term strategy and yearly plans, sharing expertise and efforts within the NEMO System Team: the core team of NEMO developers in order to ensure the successful and sustainable development of the NEMO System as a well-organised, state-of-the-art ocean model code system suitable for both research and operational work</p>

scholarly journals Striations, integrals, hourglasses, and collapse – thermal instability driven magnetic simulations of molecular clouds

2020 ◽  
Vol 500 (3) ◽  
pp. 2831-2849
Author(s):  
C J Wareing ◽  
J M Pittard ◽  
S A E G Falle
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Adaptive Mesh Refinement ◽  
Thermal Instability ◽  
Initial Conditions ◽  
Power Spectra ◽  
Adaptive Mesh ◽  
Spherical Cloud ◽  
Field Lines ◽  
Self Gravity

ABSTRACT The MHD version of the adaptive mesh refinement (AMR) code, MG, has been employed to study the interaction of thermal instability, magnetic fields, and gravity through 3D simulations of the formation of collapsing cold clumps on the scale of a few parsecs, inside a larger molecular cloud. The diffuse atomic initial condition consists of a stationary, thermally unstable, spherical cloud in pressure equilibrium with lower density surroundings and threaded by a uniform magnetic field. This cloud was seeded with 10 per cent density perturbations at the finest initial grid level around n = 1.1 cm−3 and evolved with self-gravity included from the outset. Several cloud diameters were considered (100, 200, and 400 pc) equating to several cloud masses (17 000, 136 000, and 1.1 × 106 M⊙). Low-density magnetic-field-aligned striations were observed as the clouds collapse along the field lines into disc-like structures. The induced flow along field lines leads to oscillations of the sheet about the gravitational minimum and an integral-shaped appearance. When magnetically supercritical, the clouds then collapse and generate hourglass magnetic field configurations with strongly intensified magnetic fields, reproducing observational behaviour. Resimulation of a region of the highest mass cloud at higher resolution forms gravitationally bound collapsing clumps within the sheet that contain clump-frame supersonic (M ∼ 5) and super-Alfvénic (MA ∼ 4) velocities. Observationally realistic density and velocity power spectra of the cloud and densest clump are obtained. Future work will use these realistic initial conditions to study individual star and cluster feedback.

scholarly journals Structure and Dynamics of Magnetized Dark Molecular Clouds

2012 ◽  
Vol 10 (H16) ◽  
pp. 386-386
Author(s):  
P. S. Li ◽  
C. F. McKee ◽  
R. I. Klein
Keyword(s):  
Magnetic Fields ◽  
Adaptive Mesh Refinement ◽  
Molecular Clouds ◽  
Large Scale ◽  
Dynamical Evolution ◽  
Adaptive Mesh ◽  
Magnetized Plasma ◽  
Filamentary Structure ◽  
Structure And Dynamics ◽  
Self Gravity

Massive infrared dark clouds (IRDCs) are believed to be the precursors to star clusters and massive stars (e.g. Bergin & Tafalla 2007). The supersonic, turbulent nature of molecular clouds in the presence of magnetic fields poses a great challenge in understanding the structure and dynamics of magnetized molecular clouds and the star formation therein. Using the high-order radiation-magneto-hydrodynamic adaptive mesh refinement (AMR) code ORION2 (Li et al. 2012), we perform a large-scale driven-turbulence simulation to reveal the 3D filamentary structure and dynamical state of a highly supersonic (thermal Mach number = 10) and strongly magnetized (plasma β=0.02) massive infrared dark molecular cloud. With the high resolution afforded by AMR, we follow the dynamical evolution of the cloud in order to understand the roles of strong magnetic fields, turbulence, and self-gravity in shaping the cloud and in the formation of dense cores.

scholarly journals Physical effects on compact high-velocity clouds in the circumgalactic medium

2020 ◽  
Author(s):  
Bastian Sander ◽  
Gerhard Hensler
Keyword(s):  
High Velocity ◽  
Thermal Conduction ◽  
Adaptive Mesh Refinement ◽  
Adaptive Mesh ◽  
Pressure Balance ◽  
Low Mass ◽  
Rayleigh Taylor Instability ◽  
High Velocity Clouds ◽  
Circumgalactic Medium ◽  
Self Gravity

Abstract We numerically investigate the evolution of compact high-velocity clouds (CHVCs) passing through a hot, tenuous gas representing the highly-ionized circumgalactic medium (CGM) by applying the adaptive-mesh refinement code Flash. The model clouds start from both hydrostatic and thermal equilibrium and are in pressure balance with the CGM. Here, we present 14 models, divided into two mass categories and two metallicities each and different velocities. We allow for self-gravity and thermal conduction or not. All models experience mass diffusion, radiative cooling, and external heating leading to dissociation and ionization. Our main findings are: 1) self-gravity stabilizes clouds against Rayleigh-Taylor instability which are disrupted within 10 sound-crossing times without; 2) clouds can develop Jeans-instable regions internally even though they are initially below Jeans mass; 3) all clouds lose mass by ram pressure and Kelvin-Helmholtz instability; 4) thermal conduction substantially lowers mass-loss rates, by this, extending the clouds’ lifetimes, particularly, more than doubling the lifetime of low-mass clouds; 5) thermal conduction leads to continuous, filamentary stripping, while the removed gas is heated up quickly and mixes efficiently with the ambient CGM; 6) without thermal conduction the removed gas consists of dense, cool, clumpy fragments; 7) thermal conduction might prevent CHVCs from forming stars; 8) clouds decelerated by means of drag from the ambient CGM form head-tail shapes and collapse after they reach velocities characteristic for intermediate-velocity clouds. Conclusively, only sophisticated modelling of CHVCs as non-homogeneous and non-isothermal clouds with thermal conduction and self-gravity explains observed morphologies and naturally leads to the suppression of star formation.

Sign in / Sign up

Export Citation Format

Share Document