Goals and Deliverables

The primary goal of the workshop is to bring together scientists with expertise on different physical effects, who are using different tools -- simulations, lab measurements, astronomical observations -- to understand the effects.  We will assess our current understanding of each physical effect and our ability to mitigate residual biases due to the effect -- i.e., corrections beyond those currently planned by the project. We will compare the expected residual biases to the WL requirements.  This analysis will inform priorities and strategies for future studies. 

As an example, the intrinsic on-sky shape of a galaxy is degraded and modified by the combination of atmospheric effects, optical aberrations, and detector effects listed above.  Measurements of the PSF obtained from stars must additionally be interpolated to the locations of galaxies, which is particularly challenging given the stochastic nature of the atmosphere.  One deliverable from the workshop will be a plan and tasks to be completed in the exploration of optimal estimators and the use of statistical prior knowledge of atmospheric properties in the PSF reconstruction.  Importantly, this workshop gives an opportunity to jointly address atmospheric and CCD-based PSF systematics, since they are not independent in the raw data. 

The different LSST cosmological probes -- each with its own sensitivity to these effects -- can be undertaken with the same survey data. When combined with CMB anisotropy data these WL, BAO, and clustering probes can break degeneracies (some of which are foregrounds). This workshop will explore methods of combining the measurements of the foreground systematics in these multiple probes in a joint analysis. Rather than relying on Fisher matrix approaches, more realistic data models spanning a range of systematics can be explored in an analysis of the sensitivity of residual systematics to these auxiliary data. Another deliverable of this workshop is a clear plan for that analysis, and associated tasks.

This workshop fills an unmet need of the LSST DESC: collaboration on cross-cutting tasks to identify and correct residual foreground systematics. The overall workshop deliverable will be a report outlining proposed solutions and immediate tasks to be undertaken [see WORKSHOP OUTCOMES SUMMARY].