Defining Custom Properties¶
We have previously given examples how to analyse SAGE properties at a single snapshot or over multiple redshifts. However, it is quite common that you may wish to calculate properties different to those included in the base version of sage-analysis. For example, you may wish to investigate the time since a last major merger as a function of galaxy stellar mass.
This page outlines how sage-analysis can be used to calculate any arbirtary properties.
Default Properties¶
The sage-analysis package includes a number of properties that can be analysed and plotted by default.
| Property | Plot Toggle Name | Description | Property Type |
|---|---|---|---|
| Stellar mass function | SMF | Number of galaxies with a given stellar mass. | Binned. |
| Baryonic mass function | BMF | Number of galaxies with a given stellar plus cold gas mass. | Binned |
| Gas mass function | GMF | Number of galaxies with a given cold gas mass. | Binned. |
| Baryonic Tully-Fisher | BTF | Maximum velocity of a galaxy as a function of baryonic (stellar plus cold gas) mass. | Scatter. |
| Specific star formation rate | sSFR | Specific star formation rate as a function of stellar mass. | Scatter. |
| Gas fraction | gas_frac | Fraction of baryons (stellar plus cold gas) in the form of cold gas as a function of stellar mass. | Scatter. |
| Mass metallicity | metallicity | Metallicity as a function of stellar mass. | Scatter. |
| Black hole bulge | bh_bulge | Mass of galaxy black hole as a function of galaxy bulge mass. | Scatter. |
| Quiescent galaxy population | quiescent | Fraction of galaxies that are quiescent as a function of stellar mass. | Binned. |
| Bulge fraction | bulge_fraction | Fraction of stellar mass in the form of bulge/disk as a function of stellar mass. | Scatter. |
| Baryon fraction | baryon_fraction | Baryon fraction in each reservoir (cold, hot, stellar, ejected, intracluster, and black hole) as a function of FoF halo virial mass. | Binned. |
| Reservoir mass | reservoirs | Amount of mass in each reservoir (cold, hot, stellar, ejected, intracluster, and black hole) as a function of FoF halo virial mass. | Scatter. |
| Spatial distribution | spatial | Spatial distribution of galaxies across the simulation box. | Scatter. |
There are also a handful of toggles available to analyse properties over a number of redshifts.
| Property | Plot Toggle Name | Description | Binning Type |
|---|---|---|---|
| Stellar mass function | SMF_z | Number of galaxies with a given stellar mass over multiple redshifts for each model. | Binned. |
| Star formation rate density | SFRD_z | Total star formation rate density across entire simulation box as a function of redshift. | Single. |
| Stellar mass density | SMD_z | Total stellar mass density across entire simulation box as a function of redshift. | Single. |
Adding Your Own Properties¶
There are
- Set up Model.properties[“fff”] field.
- Write the function to compute the property.
- Add the function to the calculations dict.
- Add the plotting function to the plot dict.
SAGE operates by allowing each processor to write to its own file as
galaxies are evolved through cosmic time. sage-analysis processes galaxy
properties of each of these files individually. After calculating each
property, they are stored in the
properties attribute and carried across
files. The pseudo-code looks like this:
for file in num_files:
compute stellar mass function for file
add stellar mass function to Model.properties["SMF"] array.
calculate black hole bulge relationship for file
extend the Model.properties["bh_mass"] and Model.properties["bulge_mass"] lists
...complete for other properties...
To calculate each of these properties, a function named calc_<property_name> is
called; for example, calc_SMF() is called to
compute the stellar mass function of each SAGE file.