Probing cosmology with QUaD: Scientific optimization of an experiment to measure the polarization of the Cosmic Microwave Background. by Melanie Bowden A thesis submitted to the University of Wales for the degree of Doctor of Philosophy UMI Number: U584672 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Publishing UMI U584672 Published by ProQuest LLC 2013. Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 DECLARATION This work has not previously been accepted in substance for any degree and is not being concurrentlylcurrentiy submittedsubmitted inp candidaturecan for any degree. Signed D ate.... STATEMENT 1 The QUaD project is a collaboration between a number of instutioos involving a large number of people involved in the instrument design and manufacture and the data analysis pipeline. 1 have been involved only in the data analysis and science analysis and have played no part in the experimental side of the project. The work presented in this thesis is all my own work carried out under the supervision of Prof. Walter Gear (and in close collaboration with Dr. Andy Thylor and Dr. Ken Ganga) with the exception of the following: The sensitivity calculation was based on previous calculations by Prof. Walter Gear, Dr. Jamie Bode and Prof. Sarah Church. Initial versions of the Fortran code for the area optimization and parameter estimation were given to me by Dr. Andy Taylor. The code for plotting error ellipses was written by Dr. Andy Taylor. An initial version of the time-ordered data simulation code was given to me by Dr. Ken Ganga. The estimated foreground maps and sky coverage plots were made by Dr. Ken Ganga (although these have been modified slightly). The IDL software to plot the maps was written by Dr. Ken Ganga. I acknowledge the use of the CMBFAST code for making realizations of the CMB power spectra and the HEALPix CMB package was used extensively for the work in Chapters 6 and 7. I also acknowledge the use of foreground prediction code available at http://w^ ^ b ^ .upenp^edu/^max/foregrounds.html. D ate....... STATEMENT 2 I hereby give consent for my thesis, if accepted, to be available for photocopying and for inter-library loan, and for the title and summary to be made available to outside organisations. l Signed .......... Date <^£2.0..t./A£.-........ Acknowledgements This work has carried as part of the QUaD project and throughout the course of my PhD I have received help and advice from many people within the collaboration. I thank my supervisor Walter Gear for his support, particularly in the initial stages of the work, and for reading through the drafts of this thesis under tight time constraints. This work would not have been possible without the help of Andy Taylor who provided the ideas for the survey area and parameter estimation calculations and has given me numerous crash courses on cosmology, data analysis and statistics and invaluable help with applying for jobs and writing papers. Ken Ganga has given me continual help with the survey design and data simulations and has also been a constant source of moral support. I thank Mike Zemcov for his help with the data simulations, for letting me use the results of his map-making code and for useful discussions throughout the last year, Si­ mon Melhuish for looking after my computer and for his tips on how to use the English language, Tim Waskett for help with formatting this thesis and Ian Bacchus for bringing me Diet Coke. Phil Mauskopf has provided me with the motivation to still be interested in cosmology when it has started to fade away. Finally, I would like to thank Douglas for his emotional support throughout the last three years and for explaining to me how instrumentation works. Contents 1 Introduction 3 1.1 The CM B .................................................................................................................. 4 1.1.1 The CMB in a smooth U niverse ............................................................... 4 1.1.2 The CMB temperature anisotropies ........................................................ 10 1.1.3 Observing the CMB ................................................................................... 21 1.1.4 Initial conditions - inflation ..................................................................... 24 1.1.5 Status of CMB temperature observations............................................... 28 1.1.6 Key p o in ts ....................................................................................................... 31 1.2 The polarization of the CMB .............................................................................. 33 1.2.1 The Stokes p a ra m e te rs ................................................................................ 33 1.2.2 E-B decom position ...................................................................................... 35 1.2.3 Generation of CMB polarization ............................................................... 40 1.2.4 Calculating the polarization at recombination ......................................... 43 1.2.5 Secondary polarization anisotropies ......................................................... 43 1.2.6 Degeneracy b re a k in g ................................................................................... 48 1.2.7 Key p o in ts ....................................................................................................... 50 1.3 Thesis overview ......................................................................................................... 51 2 The QUaD experiment 53 2.1 Measuring CMB polarization with QUaD ............................................................. 53 2.2 The QUaD in s tru m e n t........................................................................................... 57 2.2.1 Telescope and o p t i c s ................................................................................... 57 2.2.2 Focal plane and feed horns ......................................................................... 58 2.2.3 Cryogenics ....................................................................................................... 59 2.2.4 Detectors ....................................................................................................... 62 2.2.5 Electronics ....................................................................................................... 64 2.3 Other CMB polarization experiments ................................................................. 66 2.3.1 Detections and upper l i m i t s ...................................................................... 66 2.3.2 Experiments currently in operation ............................................................. 69 CONTENTS 2.3.3 Upcoming experiments ................................................................................ ‘u 2.3.4 Planned next generation experiments ..................................................... 71 3 Astrophysical foregrounds 73 3.1 D u s t ............................................................................................................................. 76 3.2 Synchrotron ................................................................................................................ 79 3.3 Free-free em ission....................................................................................................... 82 3.4 Point sources ............................................................................................................. 82 3.5 Conclusions and Outlook ......................................................................................... 64 4 Sensitivity calculation 87 4.1 Formalism for describing random no ise ................................................................ 87 4.2 Contribution to the NEP for a bolometric experiment ........................................ 90 4.3 Derivation of photon noise for a P S B .................................................................. 91 4.4 Calculating QUaD sensitivity ................................................................................... 94 4.5 Results.......................................................................................................................... 97 5 Forecasting performance of QUaD 101 5.1 Parameter estimation theory ..................................................................................... 101 5.1.1 The likelihood function ..................................................................................101 5.1.2 Confidence limits and the Fisher matrix .................................................103 5.2 Application to CMB polarization ........................................................................... 107 5.3 Multipole coverage ..................................................................................................... 110 5.4 Including foreground models .....................................................................................I l l 5.5 Determining area of sky to observe ......................................................................