Mapping Submillimetre Polarization with BLASTPol by Steven James Benton A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Graduate Department of Physics University of Toronto c Copyright 2015 by Steven James Benton Abstract Mapping Submillimetre Polarization with BLASTPol Steven James Benton Doctor of Philosophy Graduate Department of Physics University of Toronto 2015 The Balloon-borne Large Aperture Submillimetre Telescope for Polarimetery (BLAST- Pol) observes the linearly polarized emission from interstellar dust. Dust polarization traces magnetic fields, and submillimetre wavelengths can see into the dense molecular clouds in which stars are born. With this measurement, BLASTPol can help resolve long-standing questions about the role of magnetic fields in the beginning of star forma- tion. BLASTPol is a 1.8 m telescope with 288 Herschel/SPIRE-heritage bolometric de- tectors at 250 µm, 350 µm, and 500 µm. Polarimetric capability was added with pho- tolithographed grids and a stepped half-wave plate. This work outlines the instrument, with a focus on the BLASTbus electronics system for detector readout, telescope attitude control, and cryogenic housekeeping. In December 2010 and in December 2012, BLASTPol had two long duration balloon flights. An improved map making procedure has been used for reducing the 2012 dataset to maps of the polarized sky. The overall data analysis procedure is described, along with details of the map maker characterization. Finally, maps are presented for the seven targets observed during the 2012 flight. The 14 square degree map of the Vela C giant molecular cloud is of particularly high quality and will be used in several upcoming studies of dust physics and star formation. ii Acknowledgements I am very fortunate to have had an advisor with ceaseless enthusiasm, amazing intuition, and constant availability. Thank you, Barth. BLASTPol and Spider are large projects, in which numerous people have invested their time and energy. Thank you all. Thank you to the field teams for sharing the long struggles, the silliness, the occasional successes, and many great times. Special thanks to my local companions on both teams: Laura, Juan, Natalie, and Jamil. And to Tristan, for adventuring with me. The staff of the Physics Electronics Resource Center, especially Rob, have allowed me to accomplish much more than I could alone. The Columbia Scientific Balloon Facility team do their job so well that the risky business of ballooning seems like a reasonable choice. Computations were performed on the GPC supercomputer at the SciNet HPC Consortium. Thank you to my roommates for being there, to my friends and family who will never read this, and to my mom who will try. iii Contents 1 Introduction 1 1.1 Star Formation, Magnetic Fields, and Turbulence . .1 1.2 Measuring Magnetic Fields . .2 1.3 BLASTPol . .4 1.4 My Thesis Work . .5 1.4.1 Other Experiments . .6 2 BLASTPol Overview 7 2.1 The BLASTPol Instrument . .7 2.1.1 Optics . .7 2.1.2 Detectors . .9 2.1.3 Polarization . .9 2.1.4 Cryogenics . 13 2.2 Gondola . 14 2.2.1 Pointing . 15 2.2.2 Power System . 16 2.2.3 Computers and Electronics . 16 2.2.4 Commanding and Telemetry . 17 2.3 Scan Strategy . 18 2.4 2012 Flight . 20 2.4.1 Observation Targets . 22 3 The BLASTbus Electronics 24 3.1 The BLASTbus . 24 3.2 PCI Controller . 27 3.2.1 External synchronization . 28 3.3 Design of Second Generation System . 29 3.4 Motherboards and Crates . 30 3.4.1 Software and Firmware . 32 3.5 Daughterboards . 32 3.5.1 Analog Input (ADC) Daughterboard . 32 3.5.2 Digital I/O Daughterboard . 33 3.5.3 Analog Output (DAC) Auxiliary Boards . 35 3.6 NTD-Ge Bolometer Readout . 37 3.7 Attitude Control . 40 iv 3.8 Cryogenic Housekeeping . 41 3.9 Status and Future of the BLASTbus . 44 4 Map Making Theory 45 4.1 Polarization Overview . 45 4.1.1 Stokes Parameters . 45 4.1.2 Mueller Matrices . 47 4.2 Polarimeter Data Model . 48 4.2.1 Simple Polarimeter . 48 4.2.2 Polarization Efficiency and Half-Wave Plates . 49 4.2.3 Instrumental Polarization . 51 4.2.4 Non-ideal Half-Wave Plates . 52 4.3 Map Maker Formalism . 53 4.3.1 Linear Model . 53 4.3.2 Solving for the Map . 54 4.3.3 Naive Map Making . 56 4.3.4 Generalized Least Squares (GLS) Noise Model . 58 4.3.5 Iterative Map Making . 59 4.3.6 Preconditioned Conjugate Gradient Method . 60 5 BLASTPol 2012 Data Analysis 64 5.1 Pre-Flight Calibrations . 65 5.1.1 Polarization Calibrations . 65 5.2 Merging Datasets and Defining Chunks . 66 5.3 Pointing Solution . 67 5.4 Detector Cleaning . 68 5.4.1 Despiking . 68 5.4.2 Deconvolution . 70 5.4.3 TDRSS Pickup . 70 5.4.4 Preprocessing . 73 5.5 Pointing Offsets . 73 5.6 Detector Gain Adjustment . 74 5.7 Telescope Non-Idealities . 79 5.7.1 Beam Shape . 79 5.7.2 Instrumental Polarization . 81 6 BLASTPol Map Making 84 6.1 BLASTPol Map Making Software . 84 6.2 Noise Model . 85 6.2.1 Initial Estimate . 86 6.2.2 PSD Parametrization . 86 6.2.3 Noise Stationarity, Improved Estimate . 88 6.2.4 Correlated Noise Between Detectors . 91 6.3 TOAST Characterization . 94 6.3.1 Transfer Function . 94 v 6.3.2 Comparison to Planck . 96 6.3.3 Polarization Angle Comparison with SPARO . 96 6.3.4 Effects of Detector Correlated Noise . 104 6.3.5 Calibrating the Covariance Estimate . 104 6.3.6 Computational Performance . 106 6.4 Future Work . 108 6.4.1 Asymmetric Beam Correction . 108 6.4.2 SPIDER Map Making . 109 7 BLASTPol Maps 110 7.1 Calculating Polarization Pseudo-Vectors . 110 7.1.1 Reference Regions . 110 7.1.2 Zero-point Correction with Planck HFI . 113 7.1.3 Error Bars . 113 7.1.4 Smoothing Maps and Covariances . 115 7.1.5 Noise Bias . 115 7.1.6 Data Cuts . 116 7.2 Null Tests . 117 7.2.1 Grid Angle H–V . 119 7.2.2 Array Top–Bottom . 120 7.2.3 Array Left–Right . 120 7.2.4 IP High–Low . 120 7.2.5 Time Early–Late . 131 7.2.6 Time Interleaved . 131 7.2.7 Null Test Conclusions . 137 7.3 Maps . 138 7.3.1 Vela C . 138 7.3.2 Lupus I . 140 7.3.3 Puppis . 145 7.3.4 Carina Nebula . 145 7.3.5 G331.5–0.1 . 149 7.3.6 IRAS 08470-4243 . 149 7.3.7 VY Canis Majoris . 149 8 BLASTPol Science 153 8.1 Understanding Polarization as a Tracer . 153 8.1.1 Temperature and Column Density . 153 8.1.2 Polarization Correlations . 154 8.2 Orientations of Polarization and Structures . ..