12:00–1:00 pm ERC 401
Carles Sanchez (Penn) "Pushing the limits of the Dark Energy Survey: Selecting and characterizing high redshift galaxy samples for optimal CMB lensing cross-correlations"
The combination of galaxy clustering and weak gravitational lensing from imaging galaxy surveys provides robust measurements of the amplitude of matter fluctuations in the late Universe which, when compared to model predictions using CMB information from the early Universe, become crucial tests for our cosmological model. Recently, the Dark Energy Survey (DES) presented the analysis of its Year 3 data set, exposing a hint of tension between early and late time measurements, in line with results from previous surveys. Soon, DES will present the combination of that analysis with CMB lensing information from the South Pole Telescope (SPT) and the Planck satellite, placing even tighter constraints on the cosmological model. However, the current DES galaxy samples probe the Universe at redshifts around and below z=1, while the lensing of CMB radiation happens primarily at higher redshifts. In this talk, I will present a new ongoing analysis to push the limits of DES to probe a higher redshift regime, enabling a more optimal usage of CMB lensing information. This is the first analysis of its kind, and the challenges encountered will be relevant for next generation surveys such as Rubin LSST, Roman and Euclid. Studying redshifts higher than z=1 is difficult for imaging surveys, as it requires analyzing the faintest sources, for which photometric redshifts are far more challenging, but it opens the door to an unexplored epoch in the Universe, and will provide crucial tests of the cosmological model, constraints on primordial non-Gaussianty and alternative dark energy models.