Cross-correlations in the dark energy survey: from redshift distribution inference to probes of gravity with the cosmic microwave background

Abstract

During the past decades, we have been the witnesses of unprecedented advancements in the understanding of our universe dynamics and evolution. Indeed, together with the theory General Relativity (GR) by Albert Einstein at the beginning of the 1900’s, the improvement of observational tools have led to the establishment of the standard model of cosmology the so-called ∧-cold-Dark-Matter model (∧CDM) that is so far the simplest model that describes best our universe considering observations. However, this standard model suffers from caveats, more specifically the presence in the theory of two dark components, Dark Energy and Dark Matter. Understanding the mystery behind these two components have become the leading objective of observational cosmology today, and of current experiments, as it is the case of the Dark Energy Survey (DES), that will after 5 years of observations image about 300 million galaxies with an unprecedented depth covering one eighth of the sky (5000 sq. deg.). This thesis is based on the analysis of the first year of observation of DES (DESY1) and more in particular on the use of cross-correlation techniques in cosmological analyses. Here, we expose two of different possible use of cross-correlation. Namely, we first show how cross-correlation techniques has been employed as a tool to infer redshift distribution of objects using the socalled clustering-redshift methodologies. And moreover how for the first time this techniques have entered in the cosmological analyses to correct the mean of the redshift distributions of the DESY1 galaxy catalog with shapes (the weak lensing sample) inferred by typical photometric techniques. We explain how using simulation we have evaluated systematics errors induced by our overall methodology and present the full methodology employed for redshift distribution determination of the DESY1 Weak lensing sample. In a second time, we expose how we have been using cross-correlations as a probe of ∧CDM cosmology using in one hand cross-correlation between cosmic voids identified in the DESY1 catalogs and the lensing map from the Planck satellite and on the other hand simulated ∧CDM cosmology. More specifically, recent results have suggested an excess signal in the observed void catalogs imprint in the Cosmic Microwave Background temperature maps with respect to simulated ∧CDM cosmology, we reiterate the procedure using this time the lensing maps of the CMB. After optimizing our void catalogs in simulation, looking for population of voids responsible for the more significant detection,we could detect the imprint of DESY1 cosmic voids with a significance of ~ 7 – 12ơ with a discrepancy of ~ 3 – 9ơ with respect to ∧CDM simulations.