sci(2005)1cover.qxd 11/9/05 4:52 PM Page 1 ESA-SCI(2005)1 ESA-SCI(2005)1 PLANCK LANCK The Scientific Programme P TheThe ScientificScientific ProgrammeProgramme i FOREWORD Cosmology, the science of the origin, structure, and space-time relationships of the Universe, has been transformed in the last 15 years by measurements that sometimes confirmed but often challenged cherished ideas. To cite a few examples: • Broad and deep surveys show the evolution of the large-scale distribution of matter from the distant past to the present. • Observations of the Cosmic Microwave Background confirm that the physical processes at early times are relatively simple and well understood, and that inflation, or something very like it, occurred in the past. • The abundances of light elements are close to theoretical models of early Universe nucleosyn- thesis. • Distant supernovae show that the expansion of the Universe is accelerating. When all available data are combined, a self-consistent picture of the Universe emerges that is radically different from the view 15 years ago: the Universe is flat, ∼13.7 billion years old, and contains ∼4% ordinary matter (only part of which is luminous), ∼23% ‘dark’ matter (of unknown type), and ∼73% ‘dark energy’ (responsible for the accelerating expansion, but also of unknown origin). For 40 years, the cosmic microwave background (CMB) has been the most important source of information about the geometry and contents of the Universe. Even so, only a small fraction of the information available in the CMB has been extracted to date. Planck, the third space CMB mission after COBE and WMAP, is designed to extract essentially all of the information in the CMB temperature anisotropies. Planck will also measure to high accuracy the polarization of CMB anisotropies, which encodes not only a wealth of cosmological information but also pro- vides a unique probe of the thermal history of the Universe during the time when the first stars and galaxies formed. Polarization measurements may also detect the signature of a stochas- tic background of gravitational waves generated during inflation, 10−35 s after the Big Bang. This book describes the expected scientific output of the Planck mission, both cosmological and non-cosmological. Chapter 1 summarizes the experimental concept and the operation of the satellite. Chapter 2 covers the core cosmological science of the mission, describing the measurements that Planck will make, what we expect to learn from them about the geometry and contents of the Universe and about fundamental physics, and the combination of CMB data with other data to provide additional insights. Although the primary goal of Planck is cosmology, it will survey the whole sky with an unprecedented combination of frequency coverage, angular resolution, and sensitivity, providing data valuable for a broad range of astrophysics. Chapters 3, 4, and 5 describe non-cosmological astrophysical uses of the Planck data. Chapter 3 addresses distortions of the CMB (often called “secondary anisotropies”) caused by large structures of matter formed long after the CMB decoupled from the primeval plasma . They include the effects of hot gas in galaxy clusters (the Sunyaev-Zel’dovich effect), and the effects of gravitational lensing by matter concentrations along the path of CMB photons. These effects trace the formation of structure in the Universe, and therefore offer an additional and independent source of information on the early Universe. Chapter 4 describes discrete sources of extragalactic origin whose thermal and non-thermal emission will be detected by Planck, and which can be studied also by other observatories including Herschel. Chapter 5 discusses Galactic and Solar System science. The gas and dust of the Milky Way, out of which stars are made, and which make up about 10% of the mass of the Galaxy, radiate copiously at the frequencies measured by Planck. Cloud structure and stability, star formation, and issues such as the detailed shape of the Milky Way’s magnetic field, can all be addressed. Planck will also provide a new view of cool objects in our Solar System. The guaranteed scientific return from Planck is indeed spectacular. With such a great increase in capability over previous CMB missions, however, we can also anticipate completely new science as well. As will be seen from this book, the scientific case for Planck is even stronger now than it was when the mission was first proposed a decade ago. ii Acknowledgements This book is the result of a large effort by the Planck community (which includes a large fraction of Europe’s far-infrared/submillimeter and CMB communities as well as a large number of CMB researchers from the US) to update the scientific case for the Planck mission, taking into account the spectacular achievements of the decade since the case was first made. Planck (http://www.rssd.esa.int/Planck) is a project of the European Space Agency with instruments funded by ESA member states (in particular the Principal Investigator countries: France and Italy), and with special contributions from Denmark and the United States. The general coordination and scientific-editorial effort of this book is due to G. Efstathiou (Survey Scientist for the HFI), C. Lawrence (Survey Scientist for the LFI), and J. Tauber (Project Scientist). The chapters were assembled from contributions by the whole Planck com- munity, and edited by: Chapter 1: J. Tauber, M. Bersanelli, J.-M. Lamarre Chapter 2: G. Efstathiou, C. Lawrence, F. Bouchet, E. Martinez-Gonz´alez, S. Matarrese, D. Scott, M. White Chapter 3: N. Aghanim, M. Bartelmann Chapter 4: B. Partridge, M. Rowan-Robinson, C. Lawrence, J.-L. Puget Chapter 5: M. Giard and R. Davis The members of the Planck Science Team (at the time of writing M. Bersanelli, G. Efs- tathiou, J.-M. Lamarre, C. Lawrence, N. Mandolesi, H.-U. Norgaard-Nielsen, F. Pasian, J.-L. Puget, J.-F. Sygnet, J. Tauber) supervised the effort. The development and operation of Planck depend on the dedicated efforts of many hundreds of scientists, engineers, computer scientists, and administrators. It is not possible to name them all, but we list here some of the main entities involved: The European Space Agency (ESA) Alcatel Space (Cannes), ESA’s prime contractor for Planck The Istituto di Astrofisica Spaziale e Fisica Cosmica—sezione di Bologna (leading Institute for the LFI), funded mainly by the Agenzia Spaziale Italiana (ASI) The Institut d’Astrophysique Spatiale (leading Institute for the HFI), funded mainly by the Centre National des Etudes´ Spatiales (CNES) and Centre National de la Recherche Scientifique (CNRS). The Danish Space Research Institute (leading Institute for the Planck reflectors). The Jet Propulsion Laboratory, funded by the United States National Aeronautics and Space Administration (NASA). For a complete list of the more than 40 participating scientific institutes, the reader is referred to the Home Page of the Science Team of Planck (http://www.rssd.esa.int/Planck). iii TABLE OF CONTENTS CHAPTER 1 THE PLANCK MISSION 1 1.1 OVERVIEW 1 1.2 INTRODUCTION 1 1.3 PAYLOAD 2 1.3.1 The Low Frequency Instrument (LFI) 5 1.3.1.1 The 20K cooler 8 1.3.1.2 Systematic effects 8 1.3.1.3 Polarisation 9 1.3.2 The High Frequency Instrument (HFI) 9 1.3.2.1 Cryogenic design 11 1.3.3 Telescope 12 1.4 SPACECRAFT 12 1.5 GROUND OPERATIONS AND DATA PROCESSING 14 1.5.1 Operations 14 1.5.2 Data Processing 15 1.5.2.1 Computational challenges 16 1.5.2.2 The Simulation Pipeline 17 1.5.3 Scientific Analysis 17 1.5.3.1 Deliverable Data Products 17 1.5.3.2 Data exploitation 18 1.5.3.3 Scientific management 18 1.6 ACKNOWLEDGMENTS 19 CHAPTER 2 PRIMARY CMB ANISOTROPIES 21 2.1 OVERVIEW 21 2.2 CMB Temperature Anisotropies 22 2.2.1 Introduction 22 2.2.2 The Physics of CMB Anisotropies 22 2.2.3 Statistics of the CMB Sky 24 2.2.4 Current Knowledge of CMB Anisotropies 25 2.2.5 Beyond WMAP 27 2.3 Cosmological Parameters from Planck 29 2.3.1 Parameter Degeneracies 29 2.3.2 Planck and Inflation 32 2.3.3 Planck and Polarization of the CMB 38 2.3.3.1 Decomposition of polarization maps into E and B components 39 2.3.3.2 Temperature-polarization cross-correlation 40 2.3.3.3 E-mode polarization 41 2.3.3.4 B-mode polarization with Planck 42 iv 2.3.4 Cosmological Parameters: Comparison of WMAP and Planck 45 2.4 Probing Fundamental Physics with Planck 46 2.4.1 Neutrino Physics 49 2.4.2 The Nature of Dark Energy 50 2.4.3 Isocurvature (entropy) perturbations 52 2.4.4 String Cosmology 54 2.4.4.1 Randall-Sundrum and brane world cosmologies 55 2.4.4.2 Brane inflation 55 2.4.4.3 Pre-big bang and ekpirotic scenarios 56 2.5 Non-Gaussianity: Beyond the Power Spectrum 57 2.5.1 Non-Gaussian primordial models 57 2.5.1.1 Testing specific inflationary models 58 2.5.1.2 Testing non-inflationary models 60 2.5.2 Large Scale Geometry and Topology 61 2.5.2.1 Large scale homogeneity/isotropy 61 2.5.2.2 Large scale topology 61 2.5.3 The Lowest Multipoles 61 2.5.4 Non-Gaussianity from Secondary Anisotropies 61 2.5.5 Recent Searches for non-Gaussianity 62 CHAPTER 3 SECONDARY ANISOTROPIES 67 3.1 OVERVIEW 67 3.2 GALAXY CLUSTERS 68 3.2.1 Cosmological Importance 68 3.2.2 Hot Gas in Clusters 70 3.2.3 Clusters in Different Wave Bands 72 3.2.4 Lensing clusters 73 3.2.5 Planck’s cluster sample 75 3.2.6 Cluster motion 78 3.2.7 External information 80 3.3 REIONIZATION 80 3.4 THE LARGE-SCALE MATTER DISTRIBUTION AND THE CMB 83 3.4.1 Lensing effects on the CMB 83 3.4.2 Exploitation of lensing effects 84 3.4.3 The integrated Sachs-Wolfe effect 85 3.4.4 Large-scale structure of warm and hot gas 87 CHAPTER