PZ LOR: A Summary of the Scientific Recommendations (with DM Responses)

Of the 6 LOR describing scientific use cases:

  • 1 focused on galaxies
  • 2 focused on dark energy
  • 3 focused on active galactic nuclei

The Rubin Observatory Data Management (DM) team sincerely thank everyone who wrote a PZ LOR to provide recommendations for the LSST Object catalog PZ that would benefit particular science cases. We’ve done our best to summarize these recommendations – if any are missed, please reply in the thread.

Recommendations that are within scope for the DM team (or were already in the plans or evaluation criteria; Section 4 of DMTN-049) and are likely to be achieved:

  • adopt a PZ estimator that provides PDFs, point estimates, SED/template fits, physical params, and flags
  • adopt at least one PZ estimator that can generate accurate PZ for galaxies with AGN
  • adopt a PZ estimator that performs well with imperfect priors / incomplete training sets (especially at low-z)
  • provide PZ in the Object catalog at the time of data release (i.e., no delay)
  • make all PZ-related code, inputs, metadata, etc. available (for reproducibility)
  • correct for MW dust before passing fluxes to the PZ estimator
  • provide users with a framework and tools to cross-match to non-LSST catalogs

The “Roadmap to Photometric Redshifts for the LSST Object Catalog”, DMTN-049, has been updated to include or clarify the above scientific recommendations.

Recommendations that present a challenge:

  • incorporate non-LSST, non-optical photometry into the PZ estimates
  • cross-match the LSST Objects catalogs with external data sets (e.g., an X-ray AGN catalog) and provide the results with flags and identifiers
  • release revised PZ data products every few months as new sky regions are observed
  • link Object identifiers between data releases (so users can get new host data for old alerts)
  • in the alert packets, provide:
    • host galaxy Object data (PZ, photometry, shape)
    • non-LSST survey data for host galaxies (spec-z, PZ, photometry)

These challenges are out of scope for the Rubin Construction project (and some violate the current Rubin data rights policy), and some items (such as providing cross-matched catalogs) are best left to the expertise of the science community.

However, just because an idea or data product presents a challenge, or is beyond the scope of Rubin construction and commissioning, does not mean it could never be accomplished.

Adopting and federating value-added user-generated data products, and updating algorithms in the LSST Science Pipelines, is an Operations-era (2024 and beyond) activity that will take input from the science community via the Rubin Users Committee, the Community Engagement Team, the Science Advisory Committee, and other such groups.

It is very useful to have these suggestions raised early on so that the DM team can help the science community prepare for Operations, all of the LOR providing these recommendations are much appreciated.

Questions about any of the above are encouraged to be posted as replies in this topic thread or as new topics in the “Science - Photometric Redshifts” category of the Rubin Community Forum.


AGN = active galactic nuclei
DM = Data Management
LOR = Letter of Recommendation (for PZ Estimators)
LSST = Legacy Survey of Space and Time
MW = Milky Way
PDF = posterior distribution function
PVC = Photo-z Validation Cooperative
PZ = photometric redshift(s)
SED = spectra energy distribution

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