T7: Simulating a disk galaxy:
reproducing the SK relation

Before the tutorials:

As discussed in the Lecture, there is a famous relation observed in galaxies relating the surface density of gas with the star formation rate: the so-called SK relation.

• What does the SK stand for?
• What exactly is this relation and where does it hold?

During the tutorials:

You can start from several initial conditions of idealized galaxies:

• wget https://www.usm.uni-muenchen.de/~dolag/Lille2026/T07/7320c.dat
  small galaxy (250 180 particles)
• wget https://www.usm.uni-muenchen.de/~dolag/Lille2026/T07/7318b.dat
  still small galaxy (420 822 particles)
• wget https://www.usm.uni-muenchen.de/~dolag/Lille2026/T07/7318a.dat
  medium galaxy (794 886 particles)
• wget https://www.usm.uni-muenchen.de/~dolag/Lille2026/T07/7319.dat
  large galaxy (2 337 900 particles)

Preparing the simulation:

• For compiling, switch off all things which we needed for our idealized setup. Especially, do not forget to switch off PERIODIC, NOGRAVITY, LONG_X/Y/Z in the Config.sh file.
• Now switch on COOLING and SFR and set GENERATIONS=4 in the Config.sh file and compile the code.
• Copy the TREECOOL file from the OpenGadget3 directory into your simulation directory.
• Set up the parameter file for the simulation:
  • Adapt the parameters:
    Modify InitCondFile
    Add ICFormat 1 if you’re using one of the initial-conditions files above;
    if you’re creating your own initial-conditions file, use ICFormat 2 like usual.
    Set TimeMax 1
    Set TimeBetSnapshot 0.01
    Set PeriodicBoundariesOn 0
    Set PartAllocFactor 5.5
  • Switch on the subgrid models:
    Add CoolingOn 1
    Add StarformationOn 1
    
  • Set the softening of all particles species now involved:
    Set SofteningGas 0.02
    Set SofteningHalo 0.02
    Set SofteningDisk 0.02
    Set SofteningBulge 0.02
    Set SofteningStars 0.02
    Set SofteningGasMaxPhys 0.02
    Set SofteningHaloMaxPhys 0.02
    Set SofteningDiskMaxPhys 0.02
    Set SofteningBulgeMaxPhys 0.02
    Set SofteningStarsMaxPhys 0.02
    
  • Set the proper units:
    UnitLength_in_cm 3.085678e21
UnitMass_in_g 1.989e43
UnitVelocity_in_cm_per_s 1e5
    (Alternatively remove them, as this is the default values for them)
  • You might introduce and vary the value for:
    Later, you can try to add MaxSfrTimescale 1.5 and see what is changing.
• We suggest to set ntasks=8 and cpus-per-task=4 for the optimal performance.

Solutions

Example for analyzing the simulation

• Again, modify your plotting scripts from previous tutorials
  • wget https://www.usm.uni-muenchen.de/~dolag/Lille2026/T07/show_galaxy.py
  • python3 show_galaxy.py
  You should see a movie like this
  
  Now try to plot the SK relation
  • wget https://www.usm.uni-muenchen.de/~dolag/Lille2026/T07/show_sk.py
  • python3 show_sk.py
  You should see an image like this
  

Extra

You can additionally switch on the kinetic feedback and see what happens, especially if now a galactic outflow/wind is established.

• First you need add WINDS in the Config.sh file.
• Add to the parameter file the additional parameters needed:
  WindEfficiency 2.0
WindFreeTravelMaxTimeFactor 0.025
WindEnergyFraction 0.5
WindFreeTravelDensFac 0.5
  (These are all default values and should therefore not be set explicitly.)

Useful commands

• More informations on the OpenGadget3 containers
• Start your docker session:docker run -it -v :/mnt --name opengadget3_container opengadget3:XXX
• Connect from a second shell to a running docker session:docker exec -it opengadget3_container bash
• Get the simulation code:cp -r ~/OpenGadget3 .
• Copy the config file: wget https://www.usm.uni-muenchen.de/~dolag/Hydro/Hydro/Config.sh
• Copy the parameter file: wget https://www.usm.uni-muenchen.de/~dolag/Hydro/Hydro/box.param
• Setup the environment for compiling the code: source Build/Container_build.sh
• Compile the code: make -j
• Run a simulation: mpiexec -np 2 OpenGadget3/OpenGadget3 box.param