4.14. Posterior Investigation

Phosphoros provides a tool for the visualization of multi-dimensional likelihoods and posterior distributions. It is available only in the CLI.

As a first step, users have to generate FITS files, one per source, containing the likelihood and/or the posterior distributions. This is enabled by:

• (GUI) clicking on the Output Posterior tab in the 5. Input/Output sub-panel of the Compute Redshift window;

• (CLI) setting the --create-output-likelihoods and/or --create-output-posteriors options of the compute_redshift action as YES.

The action to call the visualization tool is plot-posterior (or PP). It requires to specify the qualified name of the FITS file containing the likelihood or the posterior distribution for a specific source and the type of plot to show, by the command line:

> Phosphoros PP --f <path>/<name file> -p <plot type>

The <plot type> arguments are Ebv, Sed, Z, Sed-Z, Ebv-Z, Sed-Ebv, corresponding to 1D/2D plots of the \(E_{B-V}\) value, SED template and redshift parameters. Moreover, the argument Sed-Ebv-Z displays a 3D density plot of the three parameters.

An example of Ebv-Z plot is shown in Fig. 4.14.

Fig. 4.14 Example of Ebv-Z plot

Note

The axes collapse is done as simple addition. For a more correct (Bayesian) axes collapse, see the 1D PDF outputs from the compute_redshift action.