modelling unresolved processes in galactic-scale simulations

MotivationProcesses

Models

Modelling Unresolved Processesin Galactic-Scale Simulations

Wolfram Schmidt

Joined project proposal with Jens Niemeyer

Contributors: Harald Braun (IAG), Christoph Federrath (ITA),and Hsiang-Hsu Wang (ITA)

AG Herbsttagung, Splintermeeting ISM, Sept. 15, 2010

Wolfram Schmidt Modelling Unresolved Processes in Galactic-Scale Simulations

MotivationProcesses

Models

Motivation

1. Isolated disk galaxy simulations: ∼ 1 . . . 10 pc resolution(Robertson & Kravtsov ’08, Agertz et al. 09, Tasker &Tan ’09, Wang et al. ’10, ...)

2. Cosmological ”zoom-in” simulations of galaxies:∼ 10 . . . 100 pc resolution (Gnedin & Kravtsov ’09,Agertz et al. ’10, Governato et al. ’10, Greif et al. ’10, ...)

3. So far, fairly simple subgrid scale recipes are applied to modelcertain processes below the grid resolution scale

SPP project objective:

High-resolution galaxy simulations with subgrid scale model ofunresolved processes (turbulence, star formation, feedback, ...)to study dynamics of the turbulent multi-phase ISM


MotivationProcesses

Models

Processes

1. Star formation is tightly correlated with molecular hydrogen(e. g. Krumholz et al. ’09, based on THINGS)

2. Dynamics of molecular clouds reduces the star formationefficiency per free-fall time to εff ∼ 0.01 (e. g. Krumholz &Tan ’07), but appear to vary over MC lifetime (Murray ’10)

- regulation by internal feedback (e. g. Fall et al. ’10)or turbulence (e. g. Padoan & Nordlund ’09)?

3. Turbulence in the ISM is driven by large-scale instabilities(e. g. Klessen & Hennebelle ’09) and feedback fromsupernovae (e. g. Joung & Mac Low ’06)

4. The ISM probably has a multi-phase structure down tosubparsec scales (e. g. Audit & Hennebelle ’10)


MotivationProcesses

Models

Models

1. Multiphase model: Springel-Hernquist-type model with rateequations for cold and warm gas densities, thermal energies,and turbulent pressure (Scannapieco & Bruggen ’08, WS &Federrath ’10)

2. Model for molecular hydrogen fraction in the cold phase(Gnedin et al. ’09, Krumholz et al. ’09)

3. Dynamical star formation efficiency: Regulation by virialparameter and turbulent Mach number of cold gas clouds(Krumholz & McKee ’05, Padoan & Nordlund ’09)

4. Non-thermal SN feedback: Energy from supernova blastwaves is injected into turbulent pressure on the grid scale(Joung et al. ’09, WS & Federrath ’10)


MotivationProcesses

Models

Research at the IAG

Combining 1.-4.:

Unified subgrid scale model (Braun & WS ’10 in prep.)

Adaptively refined large eddy simultions:

Fluid-dynamical coupling between resolved and unresolvedlength scales in AMR simulations (Maier et al. ’09)

Further methodological developments are planned as part of theSFB Astrophysical Fluid Instabilities and Turbulence in Gottingen(reviewed in fall).


MotivationProcesses

Models

Computing the Turbulent PressureSolve PDE for energy of unresolved turb. velocity fluctuations inthe highly compressible regime (WS & Federrath ’10, A&A subm.):

LES of forced supersonic turublence

0.005 0.010 0.020D�L

0.005

0.010

0.020

0.050

XKsgs\

0 2 4 6 8 10t�T

0.5

1.0

1.5

XHL�Ρ0V3LΡΕ\

scale-dependence of turbulentpressure, const. dissipation rate


modelling unresolved processes in galactic-scale simulations

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