Summary

Encouraged by many people from the community we started a large community based project to test and improve the accuracy of photometric redshifts. We will focus on the following primary objectives.

Goals:

• We require controllable photo-z's for our science applications
• We want credibility for the photo-z community
• We want understanding!
  • We have qualitative understanding of (some) influencing factors
  • We need quantitative (= predictive) understanding of (most/all) factors
• We want a set of standardised test environments for future codes
• We want to rank & profile existing methods (codes, templates, additions)
• PHAT should produce the knowledge we need to do the best/required photo-z's for our science

In order to reach these goals we will have to develop techniques that can test the following aspects of photo-z's.

Tests:

• the different codes
• the different template sets
• the influence of noise
• the different approaches to galaxy photometry
• different filter sets

It is clear that we cannot address all of these issues at once, but that we will learn most if we succeed to look at the different aspects separately. Therefore, we started with a basic simulated colour catalogue based on a particular template set. In this idealised environment the differences of the codes themselves, all of them operating with this template set, are be studied. In further steps we plan to include realistic star-formation histories, noise, etc. in the simulations. The performance/agreement of different template sets can be investigated on these simulations as well. Furthermore, as a realistic benchmark we plan to use one or more of the large publicly available spectroscopic catalogues in combination with imaging data to study the influence of all the subtle aspects that are not included in the simulations.

-- HendrikHildebrandt - 07 May 2008