This package constructs observer-based lightcones from IllustrisTNG.

See related paper introducing the outputs of this code here.

The package can be installed with:

pip install light-gen

You will need the following dependencies:

numpy
astropy
h5py
multiprocessing
glob
logging
seaborn
scipy
pandas

Using the code to generate lightcones from IllustrisTNG simulations. This code is easily adaptable to other N-body simulations too. For instructions see the example notebooks provided in the examples folder and also see the template script. The code needs you to point to the sim_data_dir folder, where all the snapshots and FoF and Subfind group catalogues are provided (based on hdf5). You can download them from the official TNG website here. The sim_data_dir directory structure must be as follows.

IllustrisTNG/
 |-snapdir_98
 | |-snap_98.0.hdf5
 | |-snap_98.1.hdf5
 | `-snap_98.599.hdf5
 |-snapdir_97
 | |-snap_97.0.hdf5
 | |-snap_97.1.hdf5
 | `-snap_97.599.hdf5
 `-snapdir_78
   |-snap_78.0.hdf5
   |-snap_78.1.hdf5
   `-snap_78.599.hdf5

And for the group catalogues:

IllustrisTNG/
 |-groups_98
 | |-fof_subhalo_tab_98.0.hdf5
 | |-fof_subhalo_tab_98.1.hdf5
 | `-fof_subhalo_tab_98.599.hdf5
 |-groups_97
 | |-fof_subhalo_tab_97.0.hdf5
 | |-fof_subhalo_tab_97.1.hdf5
 | `-fof_subhalo_tab_97.599.hdf5
 `-groups_96
   |-fof_subhalo_tab_96.0.hdf5
   |-fof_subhalo_tab_96.1.hdf5
   `-fof_subhalo_tab_96.599.hdf5

Where each snapdir_XX and group_XX refers to a single TNG snapshot, and each snapshot can be divided into multiple chunck files (going from 0 to 500).

The follows notebooks run you through the main concepts and implementations of this code:

1. 01_remapping_IllustrisTNG_boxes: introduced the remapping of cuboids to construct lightcones.
2. 02_get_lightcone_geometry: implements the get_geometry.py to get the lightcone opening angles for an given observer at the edges of the lightcone.
3. 03_get_lightcone_and_central_satellities: generates lightcone shell files for individual subshells (subhalos, halos, bhs, etc) and also classifies subhalos into centrals and satellites
4. 04_applying_rotations_to_lightcone: tutorial on rotations in 3D and how you can apply it to your lightcone to center the observer on the y-z plane (x-axis is Line of Sight)

Script: main.py

You can directly run main.py after passing the sim_data_dir with the appropriate data structure within as follows.

python3 main.py 0 1 gas /path/to/sim_data_dir

This would transform the coordinates for one chunk file (there are 600/snapshot) and save the transformed coordinates in your out_data_dir path. For group (FoF halos), bh (black holes), and Subhalo (from SUBFIND) the first two int arguments specify the entire snapshots (not chuncks as done for gas and dm).

This package has been developed by Soumya Shreeram, with contributions from: Johan Comparat.

This package uses the remap.py and list7.txt files for cuboid remapping implementation, which is downloaded from http://mwhite.berkeley.edu/BoxRemap/. Additionally, see "Embedding realistic surveys in simulations through volume remapping", J. Carlson and M. White, ApJS 190(2010)311. (preprint available at arxiv:1003.3178).

If you have any question, suggestion, or need help with the code (e.g., extending to other simulations with different data formats), don't hesitate to contact the author.

If you use this code for you work, please cite the following two related papers:

1. Shreeram et al. 2025a: https://www.aanda.org/articles/aa/abs/2025/05/aa52271-24/aa52271-24.html (also available or arXiv: https://arxiv.org/abs/2409.10397).
2. J. Carlson and M. White, ApJS 190(2010)311. (preprint available at arxiv:1003.3178).