tangos

Tangos is a system for building and querying databases summarising the results of numerical galaxy simulations.

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Tangos Tutorial – Gadget+Rockstar

Initial set up

This tutorial imports a gadget-run simulation with a Rockstar halo catalogue and consistent-trees merger information.

Make sure you have followed the initial set up instructions.

Then download the raw simulation data required for this tutorial. You need two files:

required for this tutorial.

Unpack both tar files either in your home folder or the folder that you pointed the TANGOS_SIMULATION_FOLDER environment variable to.

For most Linux or macOS systems, the following typed at your bash command line will download the required data and unpack it in the correct location:

cd $TANGOS_SIMULATION_FOLDER
curl https://zenodo.org/record/5155467/files/tutorial_gadget.tar.gz?download=1 | tar -xz
curl https://zenodo.org/record/5155467/files/tutorial_gadget_rockstar.tar.gz?download=1 | tar -xz

Import the simulation

At the unix command line type:

tangos add tutorial_gadget_rockstar --min-particles 100

The process should take about a minute on a standard modern computer, during which you’ll see a bunch of log messages scroll up the screen.

Let’s pick this command apart

Note that all tangos command-line tools provide help. For example tangos --help will show you all subcommands, and tangos add --help will tell you more about the possible options for adding a simulation.

At this point, the database knows about the existence of timesteps and their halos and groups in our simulation, but nothing about the properties of those halos or groups. We need to add more information before the database is useful.

If you want to speed up this process, it can be MPI parallelised since version 1.8.

Import rockstar’s properties

At the unix command line type:

tangos import-properties Mvir Rvir X Y Z --for tutorial_gadget_rockstar

The process should take about a minute on a standard modern computer, during which you’ll see a bunch of log messages scroll up the screen.

The example command line lists a few properties, Mvir, Rvir, X, Y and Z to import from the Rockstar .list files. The added directive --for tutorial_gadget_rockstar specifies which simulation you want to apply this operation to. It’s not strictly necessary to add this if you only have one simulation in your database.

Import the merger trees

The merger trees can be imported from consistent-trees. To do this type

tangos import-consistent-trees --for tutorial_gadget_rockstar

Note that you can also use the built-in tree builder, as described in other tutorials such as the SubFind example. But compared to the default implementation, consistent trees has the significant advantage of including “phantom halos” – i.e. halos which go missing at one timestep then reappear again. These are represented by PhantomHalo objects within tangos and show up in the web merger tree tool as a dashed line.

Importing the merger tree should take a minute or so, and again you’ll see a log scroll up the screen while it happens.

Add some more interesting properties

Let’s finally do some science. We’ll add dark matter density profiles; from your shell type:

tangos write dm_density_profile --with-prerequisites --include-only="NDM()>5000" --type=halo --for tutorial_gadget_rockstar

If you want to speed up this process, it can be MPI parallelised.

Here,

Explore what’s possible

Now that you have a minimal functioning tangos database, proceed to the data exploration tutorial.