Running CAESAR

CAESAR offers three basic functions:

[1] Identify galaxies and halos, compute a wide range of properties for each object, and cross-match them.

[2] Compute photometry accounting for the line-of-sight dust extinction to each star in the object.

[3] Compute the N most massive progenitors/descendants for any galaxy or halo in another snapshot (see Progenitors docs page for usage).

Scripted

It is generally recommended to run CAESAR within a script for computing galaxy and halo properties. This allows for more precise control over the various options, looping over many files, parallelizing, etc. Here is a basic script for running member_search:

import yt
import caesar

# first we load your snapshot into yt
ds = yt.load('my_snapshot')

# now we create a CAESAR object, and pass along the yt dataset
obj = caesar.CAESAR(ds)

# now we execute member_search(), which identifies halos, galaxies, and computes
# properties (including photometry; this requires installing FSPS) on 16 OpenMP cores
obj.member_search(haloid='fof',fof6d_file='my_fof6dfile',fsps_bands='uvoir',ssp_model='FSPS',ssp_table_file='FSPS_Chab_EL.hdf5',ext_law='composite',nproc=16)

# finally we save the CAESAR galaxy/halo catalog to your desired filename
obj.save('my_caesar_file.hdf5')

member_search() options

Here is a more detailed description of the options shown above:

  • nproc: Number of cores for OpenMP parallelization. This follows the joblib convention that negative numbers correspond to using all except nproc+1 cores, e.g. nproc=-2 uses all but 1 cores. Default: 1

  • haloid: Source for particle halo ID’s. haloid='fof' uses a 3D Friends-of-Friends (3DFOF) with b=0.2 to identify halos. haloid='snap' reads halo membership info for each particle from the snapshot variable HaloID, if present. Default: ‘fof’

  • fof6d_file: Stores results of 6DFOF galaxy finder in a file for future retrieval. If file does not exist, it is created; if it exists, the galaxy membership information is read from this file instead of running the 6DFOF. Default: None

  • fsps_bands: Triggers optional photometry computation, in specified list of bands. The fsps.list_filters() command under python-fsps lists the available bands. One can also specify a string (minimum 4 characters) that will be matched to all available bands, e.g. fsps_bands=['sdss','jwst'] will compute all bands that include the phrase sdss or jwst. Default: None

  • ssp_model: Choice of FSPS, BPASS, or BC03 (Bruzual-Charlot 2003). Default: None

  • ssp_table_file: Path to lookup table for FSPS photometry. If this file does not exist or this keyword is unspecified, it will be generated; this takes some time. If it exists, CAESAR will read it in. Default: None

Command Line

NOTE: CURRENTLY, RUNNING FROM THE COMMAND-LINE IS NOT OPERATIONAL. Please use the Scripted method described above.