A Search for Cosmic Microwave Background Anisotropies on Arcminute Scales
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A Search for Cosmic Microwave Background Anisotropies on Arcminute Scales Thesis by Jack Sayers In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy California Institute of Technology Pasadena, California 2007 (Submitted December 5, 2007) ii c 2007 Jack Sayers All Rights Reserved iii Abstract This thesis describes the results of two sets of observations made in 2003 and 2004 using Bolocam from the Caltech Submillimeter Observatory (CSO), along with a description of the design and performance of the instrument. Bolocam is a large format camera consisting of 144 bolometers with an eight arcminute field of view at the CSO, and can be operated non-simultaneously at 1.1, 1.4, or 2.1 mm. All of the data described in this thesis was collected at 2.1 mm, where the individual beams are approximately one arcminute in size. The observations were made over a total of seventy-nine nights, and consisted of surveys of two science fields, Lynx and the Subaru/XMM Deep Field (SDS1), covering a total area of approximately 1 square degree. The noise properties of the maps are extremely uniform, with RMS variations in coverage of approximately 1.5% for twenty arcsecond map pixels. The point source sensitivity of the maps is approximately 100 µKCMB per beam. Fluctu- ations in emission from the atmosphere limited the sensitivity of our measurements, and several algorithms designed to remove these fluctuations are described. These algorithms also removed astronomical flux, and simulations were used to determine the effect of this attenuation on a CMB power spectrum. Assuming a flat CMB band power in , our data Cℓ corresponds to an effective angular multipole of ℓeff = 5700, with a FWHMℓ = 2800. At these scales the CMB power spectrum is expected to be dominated by anisotropies induced by the Sunyaev-Zel’dovich effect (SZE), and have a reasonably flat spectrum. Our data is consistent with a band power of = 0 µK2 , and an upper limit of < 755 µK2 at Cℓ CMB Cℓ CMB a confidence level of 90%. From this result we find that σ8 < 1.55 at a confidence level of 90%. iv Acknowledgments My parents allowed me the freedom to pursue my interests when I was younger, and provided me with the support I needed to develop those interests. With their help, my brother Ryan and I became fascinated with math and science, and we were able to push each other in a never ending quest to see who was smarter. Along the way I was fortunate to have some great teachers, especially my high school physics teacher, Bernie Gordon. As an undergraduate at the Colorado School of Mines I was blessed with amazing professors, including Ed Cecil, Willy Hereman, and James McNiel. Numerous people at Caltech have directly helped me with this project. Kathy, Diana, and Bryanne have taken care of all the logistics, and the graduate students and postdocs in the Lange and Golwala groups have been there with advice and support. Also, the CSO staff and the Bolocam team have provided countless hours of help. Sunil has shown an unbelievable amount of patience for my questions and mistakes, and I couldn’t have asked for a better advisor. And, of course, my wife Lindsey has loved and supported me throughout this process. v This thesis is dedicated to the memory of my brother Ryan (1982 - 2003) vi Contents Abstract iii Acknowledgments iv 1 Introduction 1 1.1 ABriefHistoryofCosmology . 1 1.2 Our CurrentUnderstandingof theUniverse . ...... 7 1.3 The Sunyaev-Zel’dovich Effect and Cosmology . ...... 9 1.3.1 Background................................ 9 1.3.2 Applications ............................... 12 1.3.3 CurrentObservationalStatus . 16 1.3.4 Summary ................................. 18 2 The Bolocam Instrument 20 2.1 Overview ..................................... 20 2.2 Cryogenics..................................... 20 2.2.1 Refrigerator................................ 21 2.2.2 Dewar................................... 21 2.3 Detectors ..................................... 22 2.3.1 Overview ................................. 22 2.3.2 Characterization ............................. 24 2.4 Electronics .................................... 27 2.4.1 Design................................... 28 2.5 Optics....................................... 31 2.5.1 PhysicalComponents .......................... 31 2.5.2 MeasuredPerformance. .. .. .. .. .. .. .. 37 3 Observations and Performance 44 3.1 ObservingSite .................................. 44 vii 3.1.1 Telescope ................................. 44 3.1.2 TypicalConditions............................ 44 3.1.3 ActualConditions ............................ 46 3.2 ObservingStrategy............................... 48 3.2.1 ScienceFields............................... 48 3.2.2 ScanPattern ............................... 50 3.3 Contrasts Between 2003 and 2004 . 51 3.4 PointingReconstruction . 52 3.4.1 Relative Beam Offsets . 52 3.4.2 Developing a Model of the Array Center Location . 53 3.4.3 Uncertainties in the Pointing Model . 56 3.5 FluxCalibration ................................. 59 3.5.1 OverallTheory .............................. 61 3.5.2 Relative Calibration of the Detectors . ..... 64 3.5.3 AbsoluteCalibration. 67 3.5.4 Uncertainty in the Flux Calibration . 70 3.5.5 DerivedSourceFluxes .......................... 71 3.6 BeamProfiles................................... 75 3.6.1 Overview ................................. 75 3.6.2 ConsistencyTests ............................ 77 3.6.3 Results .................................. 81 4 Noise 85 4.1 PhotonNoise ................................... 85 4.1.1 Theory .................................. 85 4.1.2 MeasuredValues ............................. 86 4.2 Bolometer and Electronics Noise . 91 4.2.1 BolometerNoise ............................. 91 4.2.2 ElectronicsNoise ............................. 92 4.3 Non-OpticalNoise ................................ 95 4.4 Extra Noise During the 2004 Observing Season . ...... 97 4.5 AtmosphericNoise:Theory . 97 viii 4.5.1 Kolmogorov/Thin-Screen Model . 100 4.5.2 Comparison to Data: Instantaneous Correlations . ....... 101 4.5.3 Comparison to Data: Time-Lagged Correlations . 105 4.5.4 ComparisontoData: Summary. 108 4.6 AtmosphericNoise:Removal . 108 4.6.1 Average Template Subtraction . 108 4.6.2 WindModel ............................... 112 4.6.3 Higher-Order Template Subtraction . 112 4.6.4 Adaptive Principal Component Analysis (PCA) . 117 4.6.5 Nearest-Neighbor Bolometer Correlations . 117 4.7 Sensitivity Losses Due to Correlations and Atmospheric Noise . 119 4.8 Atmospheric Noise as a Function of Atmospheric Opacity . ......... 125 4.9 SummaryofAtmosphericNoise . 127 5 Data Processing 129 5.1 Merging and Parsing the Data Time-Streams . 129 5.2 FilteringandDown-Sampling . 130 5.3 NoiseRemoval .................................. 131 5.3.1 Observations of Bright Point-Like Sources . 134 5.3.2 Observations of Science Fields . 135 5.4 MapMaking ................................... 135 5.4.1 LeastSquaresMapMakingTheory. 135 5.4.2 The Bolocam Algorithm: Theory . 137 5.4.3 The Bolocam Algorithm: Implementation . 141 5.5 TransferFunctions ............................... 144 5.6 OptimalSkySubtraction . 150 5.7 FinalMapProperties.............................. 153 5.7.1 NoisePSDs ................................ 154 5.7.2 Astronomical Signal Attenuation . 154 5.7.3 Noise from Astronomical Sources . 157 6 Science Analysis 166 6.1 Procedure..................................... 166 ix 6.2 CMBAnisotropyResults . .. .. .. .. .. .. .. .. 171 6.3 SZE-InducedCMBAnisotropyResults . 175 6.4 Conclusions .................................... 178 7 Other Bolocam Science 181 7.1 Surveys for Dusty Submillimeter Galaxies . ....... 181 7.2 MolecularCloudSurveys. 183 7.3 Targeted Cluster Observations . 183 Bibliography 187 A Astronomical Flux and Surface Brightness Conversion Factors 209 B Data Synchronization 211 B.1 Data Acquisition System Multiplexer . 211 B.2 Aligning the Telescope and DAS Computer Data Streams . ....... 214 B.2.1 Results .................................. 214 B.2.2 Details of the Simulation . 216 C Computing Power Spectra and Cross Power Spectra 218 D Atmospheric Noise Removal Algorithms 222 D.1 Average/Planar/Quadratic Subtraction . ....... 222 D.2 AdaptivePCASubtraction . 223 E Data Processing: Signal Attenuation Versus Signal Amplitude 227 E.1 Theory....................................... 227 E.2 ResultsFromSimulations . 229 F Algorithm for Calculating An Excess Map Variance 234 x List of Figures 1.1 Hubble’s velocity versus distance plot . ....... 2 1.2 Primordial light element abundances . ...... 3 1.3 COBEspectrumoftheCMB .......................... 4 1.4 Current CMB power spectrum measurements . .... 6 1.5 SpectralshiftcausedbytheSZE . 11 1.6 SZEdistortionoftheCMB .. .. .. .. .. .. .. .. 12 1.7 CosmologywiththeSZE............................. 15 1.8 SZEImageofCL0016+1609. 17 1.9 SuZIEIIclusterspectra . .. .. .. .. .. .. .. 18 2.1 Bolocamrefrigerator .. .. .. .. .. .. .. .. 22 2.2 TheBolocamdewar ............................... 23 2.3 Photograph of the Bolocam detector array . ...... 23 2.4 Mapping speed versus bolometer thermal conductance . ......... 26 2.5 Bolometerparameters . .. .. .. .. .. .. .. .. 27 2.6 Simplified schematic of the Bolocam electronics . ......... 28 2.7 Photograph of the Bolocam dewar . 30 2.8 Integratingcavity............................... 32 2.9 TheBolocamhorn-plate . .. .. .. .. .. .. .. .. 32 2.10 An image of Bolocam mounted at the CSO . 34 2.11 Schematic of Bolocam optics box . 35 2.12 Bolocamopticalsystem . 36 2.13 Bolocam spectral transmission