Advanced CosmologicalSimulations

John Wise (Georgia Tech)
Enzo Workshop
北海道⼤大学 – 19 Nov 20141

Hydrodynamics with an Adiabatic Equation of State• We just ran a 323 AMR simulation with hydrodynamics and N-body dynamics.
• Go to the run directory. For example• cd ~/sapporo_cosmo/Adiabatic• Let’s analyze it.
• Projections• Phase plots in density and temperature2

Hydrodynamics with an Adiabatic Equation of State• source /mnt/iscsi5/enzo_workshop/yt-x86_64/bin/activate• We will be using the yt script, anyl.py3Hydrodynamics with an Adiabatic Equation of State• Run the yt script for the last dataset. For example,• python ../anyl.py DD0049/DD0049• Creates the projections and phase plots and places them in pics/• Note: I have written the script so that if no argument is given, all datasets areanalyzed.
• python ../anyl.py4

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Radiative Cooling and Ultraviolet Background• Now we can add more physics to the adiabatic simulation.
~guest01/sapporo_cosmo/Cooling/cooling.enzo• Add radiative cooling and non-equilibrium chemistry.
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• Add optically-thin ultraviolet backgroundCosmology Simulations

Non-cosmology Simulations

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Different Ultraviolet Backgrounds

7Ultraviolet Background (Haardt & Madau 2012)
QSO only!

QSO + Galaxies!

Includes Lyman
series lines

8Ultraviolet Background (Haardt & Madau 2012)
HIHe IIGalaxies
QSO

Photo-ionization Rate

Photo-heating Rate
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Radiative Cooling and Ultraviolet Background• This simulation takes 50 minutes to run on my laptop with 2 cores.
• Requires the tabulated UV background in the run directory.
• ~/workshop2014/enzo_dev/input/hm12_photorates.dat• If you want to run the simulation later, you can copy the parameter file andinitial conditions files from the adiabatic simulation
cd ~/sapporo_cosmo/Coolingcp <where enzo is>/enzo.exe .
./enzo.exe -d cooling.enzo

10Radiative Cooling and Ultraviolet Background• I have copied the last output to conival. You can copy it to your directory• cp -r ~guest01/sapporo_cosmo/Cooling/DD0050 .
• Let’s inspect it!

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Radiative Cooling and Ultraviolet Background• I have also uploaded a IPython notebook to my directory.
• cp ~guest01/sapporo_cosmo/Cooling/Cooling.ipynb .

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+ Star Formation and Supernova Feedback• Let’s add more physics! Star formation and supernova feedback.
• Star Formation (original formulation: Cen & Ostriker 1992)• Overdense:⇢ > ⇢SF• Converging flow: r · v < 0• Cooling:tcool < tdyn

• Gravitational unstable (originally used, but not in the specific algorithm we’llbe using): Mcell > MJ

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+ Star Formation and Supernova Feedback• Supernova feedback is modeled with thermal energy injection

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+ Star Formation and Supernova Feedback• You can find the parameter file in• sapporo_cosmo/StarFormation/stars-fb.enzo• Star formation and feedback.
• Method 5 → 25 = 32

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+ Star Formation and Supernova Feedback22

+ Star Formation and Supernova Feedback• Star formation and feedback.
Method 5 → 25 = 32
• Method 3 (Population III stars) andmethod 5 use the same minimum
overdensity. Negative number
means units in cm-3. Positive
number is in code units.
• Critical metallicity to transition
from Population III to Population II.
For this simulation, we only want toconsider Pop II stars, so we set toa tiny_number.

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+ Star Formation and Supernova Feedback• Use metal feedback in supernova.
• Use Cen & Ostriker prescription fortime-dependent feedback.
• Dynamical time (→ avg. density) ofa sphere that accretes onto thestar particle.
• Ionizing photon luminosity (in unitsof photons / s / M⊙)• Supernova thermal energy (in unitsof erg / M⊙)• Radius of sphere where the energy
is injected (in units of pc)
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+ Star Formation and Supernova Feedback• Mass fraction of cold gas inside
the sphere that is deposited into
the star particles.
• Minimum mass (in units of M⊙) ofstar particles

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+ Star Formation and Supernova Feedback• Again, this simulation takes some time to complete. About an hour.
• I have uploaded the last output at redshift 3 and IPython notebook to• ~guest01/sapporo_cosmo/StarFormation/DD0050• ~guest01/sapporo_cosmo/StarFormation/SF.ipynb• Let’s inspect it!

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⇢ > ⇢SF

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+ Radiative Feedback• Enzo has two prescriptions to solve the radiative transfer equation:• Adaptive ray tracing• Flux limited diffusion• This allows for an inhomogenous radiation field with spatially dependent
absorption and emission coefficients.
• Can be used in conjunction with a radiation background.

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+ Radiative Feedback• Radiative transfer ON

sapporo_cosmo/RT/stars-rt.enzo• Minimum rays per cell (angularresolution)• Hydrogen photo-ionization only
• Radiation periodic boundary• Ray merging ON• Ray merging radius (in units ofseparation of source pairs)

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+ Radiative Transfer• This simulation only runs to z = 7, so we can run this simulation.
cd ~/sapporo_cosmo/RadTransfer
cp ~/enzo-stable/src/enzo/enzo.exe .
./enzo.exe -d stars-rt.enzo

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Summary• Today we have covered some advanced topics in cosmology simulations.
• Usually when doing research, it is best to introduce physics progressively tounderstand the effect of each physical process.
• We have compared the same cosmological volume with the following physics.
• Adiabatic equation of state• + Radiative cooling (H, He) and an ultraviolet radiation background• + Star formation and supernova feedback• + Stellar radiative feedback, using adaptive ray tracing37