Free Parameters of the Galaxy model

We provide a summary table collecting all the free parameters available for fitting with the tools delivered with GalaPy (both using the command line and the custom fit functionalities).

All the parameters that can be tuned by sampling the parameter space or adjusted when choosing a particular model over some other are considered free parameters. Whether to fix a parameter to some particular value or to let it vary (and therefore, to consider it one additional dimension of the parameter space to be sampled), is decided by modifying the galaxy_parameters dictionary in the parameter-file (see also Choose the fixed and free parameters).

The table below collects all of these free-parameters and, along with the keyword used to univocally refer to them, provides the default value assumed internally by GalaPy, the mathematical symbol and short description of the parameter, consistently with the paper presenting the library.

Tip

The table has the purpose to guide the user when choosing what parameters to let vary, and within what ranges. If no value nor interval of values is provided to GalaPy, the library will fix the value of the parameter to the quantity reported in the Default Value column.

Warning

Parameters marked (template) select one of the 24000 pre-computed Fritz et al. (2006) templates by snapping to the nearest point on a coarse discrete grid. Sampling over these parameters is strongly discouraged: the likelihood surface will be discontinuous and the sampler cannot explore a continuous prior volume. They should be treated as fixed configuration choices made before the fit.

Note

All the parameters that do not regulate directly the physics of the galaxy model or of the noise model and, in general, all the parameters that do not appear in the table above, are instead considered hyper-parameters.