[séminaire] Probabilistic Photometric Redshifts for Next-Generation Galaxy Surveys

by Alex Malz

Tuesday 11 Sept 2018, 11:00 → 12:00 Europe/Paris

Grand Amphi (LPSC)

Upcoming and ongoing galaxy surveys will and do produce redshift probability density functions (PDFs) in addition to traditional photometric redshift (photo-z) point estimates for numerous and faint galaxies, in lieu of unattainable spectroscopic redshifts. The storage of photo-z PDFs may present a challenge with increasingly large catalogs as we face a trade-off between the accuracy of subsequent science measurements and storage costs. I present an approach to optimizing the choice of storage parametrization for a survey producing a catalog of 1-D PDFs and demonstrate it on LSST-like photo-z PDFs. Additionally, photo-z PDFs have been at best underutilized and at worst misused in cosmological inference thus far, potentially leading to inappropriate propagation of redshift uncertainty to cosmological parameter constraints. I present a mathematically self-consistent Bayesian hierarchical model for estimating the redshift distribution function, necessary for weak gravitational lensing, based on a catalog of photo-z PDFs, and compare it with traditional methods.