My former student Alex Malz (Bochum) has been back in town to finish one of the principal papers from his thesis, the CHIPPR method for combining probabilistic outputs from cosmology surveys. Our first target was redshift probability distributions: Many surveys are producing not just photometric redshift estimates, but full probability distributions over redshift. How to use these? Many ways people naively use them (like stack them, or bin them) are incorrect, probabilistically. If you want a redshift distribution, you need to perform a hierarchical inference using them. This, in turn, requires that you can convert them into likelihoods. That's not trivial for many reasons. Our first paper on this is somewhat depressing, because of the requirements both on the redshift producer, and on the redshift user. However, it's correct! And performs better than any of the unjustified things people do (duh). I signed off on the paper today; Malz will submit during the break.
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