The Cosmic 21-cm Revolution: Charting the first billion years of our universe (AAS-IOP Astronomy)

The redshifted 21-cm signal is set to transform astrophysical cosmology, bringing a historically data-starved field into the era of Big Data. Corresponding to the spin-flip transition of neutral hydrogen, the 21-cm line is sensitive to the temperature and ionization state of the cosmic gas, as well as to cosmological parameters. Crucially, with the development of new interferometers, it will allow us to map out the first billion years of our universe, enabling us to learn about the properties of the unseen first generations of galaxies. Rapid progress is being made on both the observational and theoretical fronts, and important decisions on techniques and future direction are being made. The Cosmic 21-cm Revolution gathers contributions from current leaders in this fast-moving field, providing both an overview for graduate students and a reference point for current researchers. PRELIMS.pdf 1 Preface 11 Editor biography 12 Andrei Mesinger 12 Contributors 13 CH001.pdf 1 Chapter 1 Theoretical Framework: The Fundamentals of the 21 cm Line 15 1.1 Radiative Transfer of the 21 cm Line 15 1.2 The Spin Temperature 18 1.2.1 Collisional Coupling 18 1.2.2 The Wouthuysen–Field Effect 20 1.3 Heating of the Intergalactic Medium 26 1.3.1 The Lyα Background 27 1.3.2 The Cosmic Microwave Background 28 1.3.3 The X-Ray Background 28 1.3.4 Other Potential Heating Mechanisms 29 References 31 CH002.pdf 1 Chapter 2 Astrophysics from the 21 cm Background 32 2.1 Properties of the High-z Intergalactic Medium 32 2.1.1 The Brightness Temperature 32 2.1.2 Basics of Nonequilibrium Ionization Chemistry 33 2.1.3 Ionization and Heating around Point Sources 35 2.1.4 Ionization and Heating on Large Scales 37 2.1.5 Lyα Coupling 40 2.2 Sources of the UV and X-Ray Background 42 2.2.1 Star Formation 43 2.2.2 UV Emission from Stars 48 2.2.3 Attenuation of Stellar UV Emission by Dust 51 2.2.4 Escape of UV Photons from Galaxies 52 2.2.5 X-Rays from Stellar-mass Black Holes 53 2.2.6 X-Rays from Shocks and Hot Gas 55 2.2.7 Escape of X-Rays from Galaxies 56 2.2.8 Cosmic Rays from Supernovae 56 2.3 Predictions for the 21 cm Background 57 2.3.1 Dependence on the Ionizing Efficiency 59 2.3.2 Dependence on the X-Ray Efficiency and Spectrum 60 2.3.3 Dependence on the Lyα Efficiency 62 2.3.4 Dependence on Stellar Metallicity 63 2.3.5 Dependence on the Minimum Mass 64 2.4 Summary 66 References 66 CH003.pdf 1 Chapter 3 Physical Cosmology from the 21 cm Line 71 3.1 Introduction 71 3.2 Cosmology in the Dark Ages 72 3.2.1 Setting the Stage: The Standard Cosmological Paradigm 72 3.2.2 The Global 21 cm Signal during the Dark Ages 78 3.2.3 The Power Spectrum during the Dark Ages 79 3.3 Cosmology during the Era of Astrophysics 82 3.3.1 Isolating the Matter Power Spectrum 82 3.3.2 Redshift Space Distortions 83 3.3.3 Indirect Effects of Cosmology on the 21 cm Background 85 3.4 21 cm Cosmology in a Larger Context 86 References 87 CH004.pdf 1 Chapter 4 Inference from the 21 cm Signal 90 4.1 What Do We Actually Measure? 91 4.2 Optimal Methods for Characterizing the 21 cm Signal 91 4.2.1 Global Signal 91 4.2.2 Power Spectrum 94 4.2.3 Bispectrum 97 4.2.4 Trispectrum 98 4.2.5 One-point Statistics 98 4.2.6 Wavelets 100 4.2.7 Topological Measurements of the 21 cm Signal 100 4.2.8 Bubble-size Distributions 105 4.2.9 Individual Images 107 4.2.10 Stacked Images 108 4.2.11 Multifield Approaches 109 4.3 Modeling the 21 cm Signal 109 4.3.1 Numerical Simulations 110 4.3.2 Seminumerical and Analytic Models of the 21 cm Signal 111 4.3.3 Intelligent Sampling of the Parameter Space 112 4.3.4 Emulators 113 4.3.5 Characterizing Our Ignorance 114 4.4 Inference Methods for the 21 cm Signal 115 4.4.1 Fisher Matrices 116 4.4.2 Fixed Grid Sampling 117 4.4.3 Bayesian MCMC 118 4.4.4 Model Selection and Nested Sampling 120 4.4.5 Neural Networks 121 References 124 CH005.pdf 1 Chapter 5 21 cm Observations: Calibration, Strategies, Observables 130 5.1 Interferometry Overview 130 5.2 21 cm Observables: Power Spectra and Images 134 5.3 Interferometric Calibration and 21 cm Observations 138 5.3.1 Redundant Calibration 147 5.4 Array Design and Observing Strategies 148 5.5 Conclusions 152 5.6 Acknowledgments 152 References 152 CH006.pdf 1 Chapter 6 Foregrounds and Their Mitigation 155 6.1 What Are the Foregrounds? 155 6.1.1 Galactic Foregrounds in Total Intensity 157 6.1.2 Extragalactic Foregrounds in Total Intensity 160 6.1.3 Polarized Foregrounds 162 6.1.4 Radio Frequency Interference 164 6.2 Foreground Mitigation 164 6.2.1 Foreground Mitigation in the Data Analysis Pipeline 164 6.2.2 Foreground Avoidance and Suppression 166 6.2.3 Foreground Subtraction 171 6.2.4 Residual Error Subtraction 177 6.2.5 Polarization Leakage 178 6.3 Conclusions 179 References 180 http://adsabs.harvard.edu/abs/1982A&AS...47....1H%3C/ext-link%3E%3C/element-citation%3E%3C/ref%3E%3Cref id= 181 http://adsabs.harvard.edu/abs/1982A&AS...47....1H%3C/ext-link%3E%3C/element-citation%3E%3C/ref%3E%3Cref id= 181 CH007.pdf 1 Chapter 7 Global Signal Instrumentation 184 7.1 Introduction 184 7.2 Radiometer Basics 185 7.2.1 Antenna 185 7.2.2 Receiver 187 7.2.3 Digitzer 189 7.3 Challenges Facing Experiments 190 7.3.1 Antenna Radiation Efficiency 190 7.3.2 Antenna Transfer Efficiency 190 7.3.3 Gain Pattern 191 7.3.4 Cosmic Foregrounds 192 7.3.5 Ionosphere 193 7.3.6 Polarization 193 7.3.7 Interference 193 7.4 Précis of Design Requirements 194 7.5 Outside the Box Architectures 194 7.5.1 Single-element Sensor Radiometer 194 7.5.2 Outriggers to Fourier Synthesis Telescopes 194 7.5.3 Interferometric Methods 195 7.5.4 Zero-spacing Interferometer 195 7.5.5 Lunar Occultation 196 References 196 CH008.pdf 1 Chapter 8 Status of 21 cm Interferometric Experiments 198 8.1 Introduction 198 8.2 Early Work 200 8.3 Experimental Methodologies and Current Experiments 201 8.3.1 Giant Metrewave Radio Telescope—GMRT 202 8.3.2 Murchison Widefield Array—MWA 204 8.3.3 Low Frequency Array—LOFAR 207 8.3.4 Precision Array for Probing the Epoch of Reionization—PAPER 212 8.4 Published Results 214 8.5 Current Challenges 215 8.6 Prospects for the Future 218 8.6.1 Current Instruments 218 8.6.2 Future Instruments 218 8.6.3 Future Analyses 219 References 220 CH009.pdf 1 Chapter 9 Future Prospects 224 9.1 What Drives Future 21 cm Signal Experiment? 224 9.1.1 Limits of Current 21 cm Signal Observations 225 9.1.2 What Will Drive Future 21 cm Experiments? 228 9.2 Ground-based Interferometers 229 9.2.1 The Square Kilometre Array—SKA1&2 229 9.2.2 The Hydrogen Epoch of Reionization Array—HERA 230 9.2.3 The Large Aperture Experiment to Detect the Dark Ages—LEDA 232 9.2.4 The Low Frequency Array 2.0—LOFAR2.0 234 9.2.5 The Murchison Widefield Array Phase II 234 9.2.6 New Extension in Nançay Upgrading LOFAR—NenuFAR 236 9.3 Global Signal Experiments 237 9.3.1 The Experiment to Detect the Global EoR Signature—EDGES 237 9.3.2 The Large Aperture Experiment to Detect the Dark Ages—LEDA (Global Signal) 238 9.3.3 Shaped Antennas to Measure the Background Radio Spectrum—SARAS 238 9.4 Space-based Instruments 238 9.4.1 The Dark Ages Polarimetry Pathfinder—DAPPER 239 9.4.2 Discovering the Sky at the Longest Wavelengths—DSL 239 9.4.3 Farside Array for Radio Science Investigations of the Dark Ages and Exoplanets—FARSIDE 239 9.4.4 Netherlands–China Low Frequency Explorer—NCLE 240 9.5 The Far Future of 21 cm Cosmology 240 References 241