T12: 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:

• small galaxy
• still small galaxy
• medium galaxy (also as text file)
• large galaxy

Preparing the simulation:

• First you need to replace the file cooling.c in OpenGadget3/CoolingSfr as the tutorial version contains some typos in the cooling part.
• For compiling, switch all things of which we needed for our idealized setup. Especially,do not forget to switch off PERIODIC, NOGRAVITY, LONG_X/Y/Z and all the switches enabled for MAGNETIC in the Config.sh file.
• Now switch on COOLING and SFR 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:
    InitCondFile
ICFormat 1
TimeMax 1
TimeBetSnapshot 0.01
PeriodicBoundariesOn 0
PartAllocFactor 5.5
  • Switch on the subgrid models:
    CoolingOn 1
StarformationOn 1
    
  • Set the softening of all particles species now involved:
    SofteningGas 0.02
SofteningHalo 0.02
SofteningDisk 0.02
SofteningBulge 0.02
SofteningStars 0.02
SofteningGasMaxPhys 0.02
SofteningHaloMaxPhys 0.02
SofteningDiskMaxPhys 0.02
SofteningBulgeMaxPhys 0.02
SofteningStarsMaxPhys 0.02
    
  • Set the proper units:
    UnitLength_in_cm 3.085678e21
UnitMass_in_g 1.989e43
UnitVelocity_in_cm_per_s 1e5
    
  • Add the new parameters needed:
    CritPhysDensity 0.
MaxSfrTimescale 1.5
CritOverDensity 57.7
TempSupernova 1.0e8
TempClouds 1000.0
FactorSN 0.1
FactorEVP 1000.0
    

Solutions

• parameter file and Config.sh example files.
• Example for visualising the results
  • show_galaxy.pro in IDL
• You should see a movie like this:
  
• Example for SK relation
  • show_sk.pro in IDL
• You should see an image like this:
  
• Example using Fortran and gnuplot:
  • ifort -g -traceback -check all -fpe0 -o galaxysetup galaxysetup.f90
    (this uses galaxy.txt, which is a text version of the “small” galaxy initial conditions)
  • ./galaxysetup
  • gnuplot grid.plt (to check that the particle positions are set up correctly)
  • compile Gadget as described above, but use ICFormat 2
  • run Gadget using galaxies.ic as the initial conditions file and output as the snapshot file base in the parameter file, and BoxSize = 1
    (and TimeMax = 10, TimeBetSnapshot = 0.1)
  • ifort -g -traceback -check all -fpe0 -o readsnap readsnap.f90
  • for file in output_???; do ./readsnap $file >$file.txt; done
  • gnuplot galaxy.plt
    (this requires ffmpeg, which is installed on our ltsp machines)
  • xine -l galaxies.mp4
    
  • SK relation: figure out how to do this yourself.

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