4.5. SED weights

SED template is one of the free parameters used in the model fitting by Phosphoros. The SED axis consists in a discrete set of SEDs that map what is actually a continuous multi-dimensional space (e.g., the colors space). For each SED, Phosphoros computes a weight that quantifies the information brought by the SED with respect to the other SEDs of the library (for example, if the library contains two identical SEDs, their weights will be reduced by a factor two). Weights are then taken into account in projecting likelihood/posterior distributions.

Let’s see how SED weights are computed (a more detailed explaination can be found in the Phosphoros Paper []). Given a set of filters, for each SED template we can compute all colors associated to the filters. In this way, any SED is mapped to a set of continuous values. A distance between SEDs can be therefore straightforwardly defined in the colors space. Based on it, the area of influence of a SED in the colors space is defined as the volume of the hypercube with side equal to the maximum distance found between two SEDs. The SED weight is then defined by the volume uniquely covered by a SED (volumes are normalized such that a completely separated SED would have a volume of 1).

4.5.1. SED weights with GUI

In the 3. Priors sub-panel of the Compute Redshifts panel, users can add or discard SED weights in the redshift computation by clicking on the Add SED's weights computation control.

4.5.2. SED weights with CLI

SED weights can be computed in the CLI using the compute_sed_weights (or CSW) action. Phosphoros reads by default the configuration file:

> $PHOSPHOROS_ROOT/config/PhosphorosComputeSedWeight.conf

The configuration file for this action can be generated by the GUI clicking on Save Config. File in the Compute Redshifts panel (providing the Add SED's weights computation option is selected, see above).

An example of configuration file is:

SED-Weight-Output=<output file>
catalog-type=Quickstart
model-grid-file=Grid_QuickStart_MADAU.dat

filter-name=Quickstart/H
filter-name=Quickstart/J
filter-name=Quickstart/Y
filter-name=Quickstart/g
filter-name=Quickstart/i
filter-name=Quickstart/r
filter-name=Quickstart/vis
filter-name=Quickstart/z

The output file containing the SED weights is located by default in AuxiliaryData/GenericPriors/SedWeight/. The location can be changed including the relative path with respect to this directory.

The name of the input model-grid file is provided by the model-grid-file option. If the path is not included, the file is expected in the directory IntermediateProducts/<catalog type>/ModelGrids/.

The filters to use for the SED-weight computation can be indicated one by one as above. Alternatively, users can select all the filters present in a given directory (or group) using the option filter-group=<directory name> (where the directory is expected to be below AuxiliaryData/Filters/). Filters can be also excluded from a group by filter-exclude=<filter name>.

Warning

SED weights will be applied in the redshift computation only if the name of the SED-weight output file is provided to the compute_redshifts action through the option:

generic-grid-prior=<sed-weights output file name>