Planned Activities

Within the overarching scientific goal of detecting BAOs with LSST, the LUPM group has identified several activities to be pursued in collaboration with other members of DESC, especially in France. First, such a signal will necessitate a large-scale analysis of the survey, challenging given the size of the corresponding catalogue. This so-called “level 3" software will take time and effort to design, optimize, and implement, even if past results with other catalogues pave the road ahead. One key element here will be the redshift estimation from photometric measurements; while many photo-z codes of good quality are available, LSST will present new challenges, as does any major new instrument, so that it is important to study early enough the various possible optimizations of existing methods to the LSST needs. One possible route, which presents the added advantage of allowing newcomers in the field to familiarize themselves with optical spectra of galaxies, consists in revisiting the different galactic templates used in the past to fit photometric data to redshifted galactic spectra and thus retrieve the photo-z estimate, in view of recent publications of extensive spectroscopic atlases. But even more important to the photo-z quality is the actual accuracy of the photometry obtained with LSST, and its uniformity across the whole survey. This quality will heavily depend on three key points. First, the software producing the catalogue (so-called “level 2" software) will need to be qualified against real data. It is thus critical to perform “Data Challenges", where raw data from other instruments are reprocessed with the LSST software, an effort that LSST-France is currently largely leading. Second, the accuracy of the calibration procedure is a major challenge for LSST, and is naturally still receiving a lot of attention. One possible improvement on the baseline calibration model could result from a more global, complete, and complex use of the exquisite astrometric and photometric dataset that the Gaia satellite will provide¹. Finally, photometric accuracy is ultimately related to the in-depth understanding of the CCD sensor response. LSST-France will take part to the electro-optical acceptance testing of the camera sensors, and to their characterization. In close collaboration with LSST-France, discussions are under way with SLAC colleagues in the U.S.A. in order to contribute to this effort at the level of the framework and software implementation and deployment.