Tangos Tutorial – Black holes

This tutorial covers adding black holes and crossmatching simulations to make halo-to-halo comparisons. It extends the first steps with Changa+AHF tutorial by adding a simulation with black holes. The simulation is started from identical initial conditions and therefore serves as a comparison to quantify the effect of AGN feedback.

Download, add and process the new simulation

First, download the raw simulation data required for this tutorial. Unpack the tar file either in your home folder or the folder that you pointed the TANGOS_SIMULATION_FOLDER environment variable to.

Next, refer back to the first steps with Changa+AHF tutorial. Follow all the steps there but replacing tutorial_changa with tutorial_changa_blackholes.

Note that if you are using Michael Tremmel’s black hole implementation in Changa, you need to run his pre-processing script to generate the black hole logs (such as .shortened.orbit and .mergers) from the raw output logs.

Crosslink the simulations

Next we’ll identify which halo corresponds to which across the simulations. This allows us to make one-to-one comparisons to isolate the effects of AGN. From your UNIX shell type:

tangos crosslink tutorial_changa tutorial_changa_blackholes

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

Add properties to the black holes

Black holes are added to the tangos database with a specialised script that scans each simulation output for black hole particles. Type:

tangos import-changa-bh --sims tutorial_changa_blackholes

This scans through the timesteps, adds black holes from each snapshot, and links them together using merger information from changa’s output .mergers file.

However no properties are associated with the black holes until you ask for them. Property calculations can be applied to black holes (and other objects) in just the same way as halos, using the tangos write shell command. Type:

tangos write BH_mass BH_mdot_histogram --for tutorial_changa_blackholes --type bh

Here

• BH_mass and BH_mdot_histogram are properties referring to, respectively, the mass of the black hole at a given timestep and the recent accretion history. Note that BH_mdot_histogram is a histogram property that can be reassembled across time in different ways, like SFR_histogram.
• --for tutorial_changa_blackholes idenfities that we are only adding these properties to that particular simulation
• --type bh is a new directive, indicating the writer should be applied to all black hole objects in the simulation (rather than regular halos).

If you want to speed up the processes above, tangos import-changa-bh and tangos write can both be MPI parallelised.

Explore

Now return to the data exploration tutorials to explore what you’ve created.