Dark Energy Survey

Résumé

Le Dark Energy Survey (acronyme : DES) est un programme international de relevé optique et proche-infrarouge cherchant à cartographier des centaines de millions de galaxies dans le but de mieux comprendre la nature de l'énergie noire. De 2013 à 2019 il a utilisé le télescope Víctor M. Blanco, un télescope Ritchey-Chrétien à monture équatoriale et au miroir primaire de de diamètre, situé à l'observatoire interaméricain du Cerro Tololo (CTIO) au Chili et a permis de préparer le programme de relevé du projet DESI. Le télescope est équipé de la DECam (pour Dark Energy Camera) à son foyer principal, une caméra contenant 62 capteurs d'images avec une définition de 520 mégapixels. Objectifs scientifiques Le DES analyse la structure à grande échelle de l'univers à l'aide de quatre différents indices : les supernovae de type Ia (pour révéler l'histoire de l'expansion de l'univers), les oscillations acoustiques des baryons (pour révéler la distribution des galaxies à travers le

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https://fr.wikipedia.org/wiki/Dark_Energy_Survey

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This course presents the physical principles and the recent research developments on three topics of particle and nuclear physics: the physics of neutrinos, dark matter, and plasmas of quarks and gluons. An emphasis is given on experimental aspects in these three research fields.

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The DES-CMASS sample (DMASS) is designed to optimally combine the weak lensing measurements from the Dark Energy Survey (DES) and redshift-space distortions (RSD) probed by the CMASS galaxy sample from the Baryonic Oscillation Spectroscopic Survey. In this paper, we demonstrate the feasibility of adopting DMASS as the equivalent of CMASS for a joint analysis of DES and BOSS in the framework of modified gravity. We utilize the angular clustering of the DMASS galaxies, cosmic shear of the DES METACALIBRATION sources, and cross-correlation of the two as data vectors. By jointly fitting the combination of the data with the RSD measurements from the CMASS sample and Planck data, we obtain the constraints on modified gravity parameters mu(0) = -0.37(-0.45)(+0.47) and Sigma(0) = 0.078(-0.082)(+0.078). Our constraints of modified gravity with DMASS are tighter than those with the DES Year 1 REDMAGIC sample with the same external data sets by 29 per cent for mu(0) and 21 per cent for Sigma(0), and comparable to the published results of the DES Year 1 modified gravity analysis despite this work using fewer external data sets. This improvement is mainly because the galaxy bias parameter is shared and more tightly constrained by both CMASS and DMASS, effectively breaking the degeneracy between the galaxy bias and other cosmological parameters. Such an approach to optimally combine photometric and spectroscopic surveys using a photometric sample equivalent to a spectroscopic sample can be applied to combining future surveys having a limited overlap such as DESI and LSST.

2022

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Controlling and leveraging small-scale information in tomographic galaxy-galaxy lensing

Jonathan Andrew Blazek

The tangential shear signal receives contributions from physical scales in the galaxy-matter correlation function well below the transverse scale at which it is measured. Since small scales are difficult to model, this non-locality has generally required stringent scale cuts or new statistics for cosmological analyses. Using the fact that uncertainty in these contributions corresponds to an uncertainty in the enclosed projected mass around the lens, we provide an analytic marginalization scheme to account for this. Our approach enables the inclusion of measurements on smaller scales without requiring numerical sampling over extra free parameters. We extend the analytic marginalization formalism to retain cosmographic (shear-ratio) information from small-scale measurements that would otherwise be removed due to modelling uncertainties, again without requiring the addition of extra sampling parameters. We test the methodology using simulated likelihood analysis of a Dark Energy Survey Year 5-like galaxy-galaxy lensing and galaxy clustering datavector. We demonstrate that we can remove parameter biases due to the presence of an unmodelled one-halo contamination of the galaxy-galaxy lensing signal, and use the shear-ratio information on small scales to improve cosmological parameter constraints.

OXFORD UNIV PRESS2020

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Dark Energy Survey Year 1 results: Methodology and projections for joint analysis of galaxy clustering, galaxy lensing, and CMB lensing two-point functions

Jonathan Andrew Blazek, Eduardo Sanchez

Optical imaging surveys measure both the galaxy density and the gravitational lensing-induced shear fields across the sky. Recently, the Dark Energy Survey (DES) Collaboration used a joint fit to two-point correlations between these observables to place tight constraints on cosmology (T. M. C. Abbott et al. (Dark Energy Survey Collaboration), Phys. Rev. D 98, 043526 (2018)). In this work, we develop the methodology to extend the DES Year 1 joint probes analysis to include cross-correlations of the optical survey observables with gravitational lensing of the cosmic microwave background as measured by the South Pole Telescope (SPT) and Planck. Using simulated analyses, we show how the resulting set of five two-point functions increases the robustness of the cosmological constraints to systematic errors in galaxy lensing shear calibration. Additionally, we show that contamination of the SPT+Planck cosmic microwave background lensing map by the thermal Sunyaev-Zel'dovich effect is a potentially large source of systematic error for two-point function analyses but show that it can be reduced to acceptable levels in our analysis by masking clusters of galaxies and imposing angular scale cuts on the two-point functions. The methodology developed here will be applied to the analysis of data from the DES, the SPT, and Planck in a companion work.

2019

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