Downloading and caching Halotools-provided catalogs

This section of the documentation describes how to get up and running with the halo and particle catalogs provided by Halotools. To see if Halotools provides the catalogs you need, see the Simulations and Halo Catalogs Provided by Halotools page. If you want to use your own catalog and/or use Halotools to process an alternative catalog, see the Working with alternative halo and particle catalogs page.

Halotools provides a handful of homogeneously processed halo catalogs and associated particle data. These catalogs have been prepared into a standard form, and so once they are downloaded they will be directly added to your cache and can immediately be used for your science application.

The class responsible for downloading and caching these catalogs is DownloadManager.

>>> from halotools.sim_manager import DownloadManager
>>> dman = DownloadManager()

Below appears a summary table of the snapshots available for download. See the Simulations and Halo Catalogs Provided by Halotools for further information about the snapshots. The information in the table below can be used to select the appropriate arguments to pass to the DownloadManager.

simname available halo-finders available redshifts
bolshoi rockstar, bdm 0.0, 0.5, 0.84, 2.00
bolplanck rockstar 0.0, 0.5, 1.00, 2.00
multidark rockstar 0.0, 0.5, 1.00, 2.15
consuelo rockstar 0.0, 0.5, 1.00, 2.00

Using the convenience script

There is also a convenience script providing command-line wrapper behavior around this class: scripts/download_additional_halocat.py. Whether you use the script or the DownloadManager class, when you download the Halotools-provided catalogs, the download location will be stored in the cache log so that Halotools will remember where you stored them. For example, if you downloaded Multidark rockstar halos at z = 1, you can load this catalog into memory using the CachedHaloCatalog class:

>>> from halotools.sim_manager import CachedHaloCatalog
>>> halocat = CachedHaloCatalog(simname = 'multidark', halo_finder = 'rockstar', redshift = 1) 

The rest of this section of the documentation decribes how to use the DownloadManager class. If you prefer to use the convenience script, run it from the command line and throw the help flag to see its calling sequence:

python scripts/download_additional_halocat.py –help

Usage tutorial for the DownloadManager class

The primary functionality of the DownloadManager class lies in just two very similar methods: download_processed_halo_table and download_ptcl_table. The download_processed_halo_table method accepts three positional arguments: simname, halo_finder and redshift.

>>> from halotools.sim_manager import DownloadManager
>>> dman = DownloadManager()
>>> dman.download_processed_halo_table('bolplanck', 'rockstar', 0.5) 

The optional argument version_name can be used to specify which version of the catalogs you download, with default value set in the sim_defaults module. The purpose of the version_name is to differentiate between the same simulation data processed in different ways. Processing differences could either occur at the level of halo-finding, or simply in the cuts placed on the original halo catalog.

You can the download location with the download_dirname argument. By default, your halo catalogs will be downloaded to the Halotools cache directory:

$HOME/.astropy/cache/halotools/

You are free to store the halo catalogs in any location on disk that you like, though it will generally help ensure reproducibility if you do not move your halo catalogs around. For more information about managing the disk locations of your halo catalogs, see Relocating Simulation Data and Updating the Cache.

The download_ptcl_table method has the same API, where the only difference is that you do not specify a halo-finder when you want a particle table, as the particles were selected randomly without regard to halo membership.