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The access to the contents of this doctoral thesis it is limited to the acceptance of the use conditions set by the following Creative Commons license: https://creativecommons.org/licenses/?lang=en Dark Energy properties from the combination of large-scale structure and weak gravitational lensing in the Dark Energy Survey Author: Carles Sánchez Alonso Departament de Física Universitat Autònoma de Barcelona A thesis submitted for the degree of Philosophae Doctor (PhD) Day of defense: 28 September 2017 Director & Tutor: Dr. Ramon Miquel Pascual IFAE & ICREA Edifici Cn, UAB 08193 Bellaterra (Barcelona), Spain [email protected] CONTENTS Introduction 1 I Preliminars 3 1 Cosmological framework 5 1.1 The smooth universe ............................. 6 1.1.1 The field equations ......................... 6 1.1.2 The FLRW metric ........................... 7 1.1.3 The Friedmann equations ..................... 8 1.2 Fundamental observations ......................... 9 1.2.1 The expansion of the universe: Hubble’s law .......... 9 1.2.2 The Cosmic Microwave Background ............... 11 1.2.3 The abundance of primordial elements ............. 14 1.3 Distances in the universe .......................... 16 1.3.1 Comoving distance .......................... 16 1.3.2 Angular diameter distance ..................... 16 1.3.3 Luminosity distance ......................... 17 1.4 The accelerating universe .......................... 18 1.5 The Large-Scale Structure of the Universe ................ 19 1.5.1 Linear structure formation ..................... 19 1.5.2 The primordial power spectrum .................. 20 1.5.3 Non-linear evolution ........................ 22 1.5.4 The galaxy 2-point correlation function ............. 23 1.5.5 The galaxy bias ............................ 24 1.6 Weak Gravitational Lensing ......................... 26 1.6.1 The deflection angle ......................... 27 1.6.2 The lens equation .......................... 29 1.6.3 Distortion and magnification ................... 30 iii CONTENTS 1.6.4 The lensing convergence as the projected matter density .. 33 2 The Dark Energy Survey 35 2.1 Spectroscopic and photometric redshift surveys ............ 38 2.1.1 Spectroscopic redshift determination .............. 39 2.1.2 Photometric redshift determination ............... 40 2.2 Measuring galaxy shapes .......................... 43 II Photometric redshifts 47 3 Photometric redshifts in the DES-SV data 49 3.1 Introduction .................................. 49 3.2 DES-SV photometric sample ........................ 52 3.3 DES-SV spectroscopic sample ........................ 56 3.3.1 The weighting procedure ...................... 59 3.4 Photometric redshifts in the DES-SV calibration samples ....... 60 3.4.1 Methods ................................ 62 3.4.2 Results of the photo-z analyses .................. 72 3.4.3 Results for DESDM, TPZ, SkyNet and BPZ photo-z codes .. 85 3.5 Discussion ................................... 90 3.6 Summary and conclusions .......................... 92 III Cosmology from LSS and WL 95 4 Cosmology from large scale galaxy clustering and galaxy-galaxy lens- ing with DES-SV data 97 4.1 Introduction .................................. 97 4.2 Theory ...................................... 98 4.2.1 Non-linear bias model ........................100 4.3 Data and measurements ...........................101 4.3.1 Measurements ............................103 4.3.2 Covariances ..............................106 4.4 Fiducial Cosmological Constraints .....................108 4.5 Robustness of the results ...........................114 4.5.1 Choice of scales ............................117 4.5.2 Photo-z systematics .........................119 4.5.3 Shear calibration systematics ...................120 4.5.4 Intrinsic Alignments .........................121 4.5.5 Impact of Baryons ..........................122 iv CONTENTS 4.5.6 Impact of observing conditions ..................123 4.5.7 Low-z lens bin results ........................126 4.6 Discussion ...................................127 4.6.1 External Datasets ...........................127 4.6.2 Comparison with DES cosmic shear ...............128 4.6.3 Comparison with the literature ..................129 4.7 Conclusions ...................................130 IV Cosmic voids and void lensing 131 5 Cosmic Voids and Void Lensing in the DES-SV data 133 5.1 Introduction ..................................133 5.2 Data and simulations .............................135 5.2.1 Void tracer galaxies: the redMaGiC catalog ...........136 5.2.2 Lensing source catalog .......................137 5.3 Photo-z void finder algorithm ........................138 5.3.1 Void finder algorithm ........................138 5.3.2 Performance on simulations ....................140 5.4 DES-SV Void Catalog .............................142 5.4.1 Voids near the survey edge .....................143 5.4.2 Line of sight slicing strategy ....................143 5.4.3 Final void catalog ..........................146 5.5 Void Lensing ..................................147 5.5.1 Measurement .............................147 5.5.2 Covariance ..............................148 5.5.3 Null tests: Cross-component and randomized voids ......150 5.5.4 Tangential shear profile .......................150 5.5.5 Model fits ...............................152 5.5.6 Comparison to previous measurements .............153 5.6 Discussion ...................................154 Summary and conclusions 157 A Description of the metrics 159 B Excess Surface Density ⌃ 165 C ngmix vs. im3shape 169 D Choice of δm 171 v CONTENTS E Lensing on individual slicings 173 F Randomized void catalog 175 Bibliography 177 vi INTRODUCTION In the past century we have learned a lot about the Universe, and there are two main aspects responsible for this advance. On the one hand, the foundation of General Relativity enabled the development of a coherent, testable theory of the Universe. On the other hand, the improvement of technology and observational techniques have led to the collection of an enormous amount of data. Remarkably, there exists a model for which theory and observations are in quantitative agree- ment. This standard cosmological model, called ⇤CDM and presented in Chapter 1 of this thesis, appears to be robust and simple, but only with the addition of two components of unknown nature and origin: dark matter and dark energy. Furthermore, these two components constitute the vast majority of the energy content in the Universe. For that reason, it is of capital importance to understand these components in depth, as they may be holding the key to the discovery of new physics beyond the standard cosmological model and the standard model of particle physics. Galaxy surveys provide detailed information on the large-scale structure of the Universe, which, in turn, helps us understand its geometry, composition, evo- lution and fate. Over the past decades, these maps of the Universe have grown from thousands of galaxies in the pioneering Center for Astrophysics (CfA) Red- shift Survey (1977-1982) to several million galaxies in the Sloan Digital Sky Sur- vey (SDSS, started in 2000). In this thesis we analyze data from the Dark Energy Survey (DES), which is an ongoing imaging survey, started in 2012, that will cover about one eighth of the sky (5000 sq. deg.) to an unprecedented depth, imaging about 300 million galaxies in 5 broadband filters in the optical and near infrared parts of the electromagnetic spectrum. DES and its necessary associated tech- niques are presented in detail in Chapter 2, and that, together with the theoretical background introduced in Chapter 1, consititues Part I of this thesis. The accuracy of the science to be performed with DES and any other photo- metric galaxy survey strongly depends on the correct estimation of galaxy red- shifts, which are related to the distances to those detected galaxies. The pho- tometric redshift estimation technique, to which we devote Part II of this thesis, 1 INTRODUCTION relies purely on galaxy colors, and its associated inaccuracies constitute one of the most important sources of observational systematic uncertainties in imaging galaxy surveys and hence in modern cosmology. The principles of this technique are presented, followed by an extensive analysis of different photometric redshift estimation methods applied to DES data, including the characterization of photo- metric redshift algorithms later used for cosmological studies in DES. Naturally, galaxy surveys grant us access to the large-scale structure of the Uni- verse through the observation of the galaxy distribution. However, galaxies are not unbiased tracers of the total matter distribution, which appears to be com- posed predominantly by dark matter. Crucially, imaging galaxy surveys enable the measurement of the weak gravitational lensing effect, which produces small distortions in the shapes of distant galaxies due to the gravitational pull of fore- ground structures, and is sensitive to the total, both luminous and dark, matter distribution. The combination of galaxy clustering and weak gravitational lens-