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Observing the Galactic Plane with the Balloon-Borne Large-Aperture Submillimeter Telescope

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Observing the Galactic Plane with the Balloon-Borne Large-Aperture Submillimeter Telescope Observing the Galactic Plane with the Balloon-borne Large-Aperture Submillimeter Telescope by Anthony Gaelen Marsden M.Sc., The University of British Columbia, 2002 B.Sc., The University of British Columbia, 2000 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in The Faculty of Graduate Studies (Physics) THE UNIVERSITY OF BRITISH COLUMBIA November 2007 c Anthony Gaelen Marsden, 2007 Abstract ii Abstract Stars form from collapsing massive clouds of gas and dust. The UV and optical light emitted by a forming or recently-formed star is absorbed by the surrounding cloud and is re-radiated thermally at infrared and submillimetre wavelengths. Observations in the submillimetre spec- trum are uniquely sensitive to star formation in the early Universe, as the peak of the thermal emission is redshifted to submillimetre wavelengths. The coolest objects in star forming regions in our own Galaxy, including heavily-obscured proto-stars and starless gravitationally-bound clumps, are also uniquely bright in the submillimetre spectrum. The Earth's atmosphere is mostly opaque at these wavelengths, however, limiting the spectral coverage and sensitivity achievable from ground-based observatories. The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) observes the sky from an altitude of 40 km, above 99.5% of the atmosphere, using a long-duration scientific balloon platform. BLAST observes at 3 broad-band wavelengths spanning 250{500 µm, taking advan- tage of detector technology developed for the space-based instrument SPIRE, scheduled for launch in 2008. The greatly-enhanced atmospheric transmission at float altitudes, increased detector sensitivity and large number of detector elements allow BLAST to survey much larger fields in a much smaller time than can be accomplished with ground-based instruments. It is expected that in a single 10-day flight, BLAST will detect 10 000 extragalactic sources, ∼ 100 the number detected in 10 years of ground-based observations, and 1000s of Galactic ∼ × star-forming sources, a large fraction of which are not seen by infrared telescopes. The instrument has performed 2 scientific flights, in the summer of 2005 and winter of 2006, for a total of 16 days of observing time. This thesis discusses the design of the instrument, performance of the flights, and presents the analysis of 2 of the fields observed during the first flight. A failure in the optical system during the first flight precluded sensitive extragalactic observations, so the majority of the flight was spent observing Galactic targets. We anticipate exciting extragalactic and Galactic results from the 2006 data. Contents iii Contents Abstract . ii Contents . iii List of Tables . viii List of Figures . ix Glossary . xii Preface . xiv Acknowledgements . xv 1 Introduction . 1 1.1 Cosmic Infrared Background . 3 1.2 Star Formation History . 4 1.3 Extragalactic Submillimetre Astronomy . 5 1.3.1 Negative K-correction . 5 1.3.2 Number Counts . 7 1.3.3 Luminosity Evolution . 8 1.3.4 Clustering . 8 1.3.5 The Confusion Limit . 9 1.4 Galactic Submillimetre Emission . 9 1.5 A Simple Model . 11 1.6 BLAST . 13 1.6.1 Sensitivities and Predicted Number Counts . 13 1.6.2 Photometric Redshifts . 16 Contents iv 1.6.3 Science Goals . 16 1.7 Instrument Performance . 17 1.8 Outline . 17 2 The BLAST Instrument . 18 2.1 Detectors . 20 2.1.1 The Bolometer Device . 20 2.1.2 Thermal Model . 21 2.1.3 Responsivity . 23 2.1.4 Read-out . 25 2.1.5 Noise Properties . 25 2.2 Cryogenics . 27 2.3 Optics . 30 2.3.1 Warm Optics . 30 2.3.2 Cold Optics . 31 2.3.3 Filters . 31 2.4 Gondola Frame . 33 2.4.1 Outer Frame . 35 2.4.2 Inner Frame . 35 2.4.3 Sun Shields . 36 2.5 Pointing System . 36 2.5.1 Active Pointing . 36 2.5.2 Pointing Sensors . 46 2.6 Warm Electronics . 48 2.6.1 Data Acquisition System . 49 2.6.2 Attitude Control System . 51 2.6.3 Flight Computers . 51 2.7 Power System . 52 2.7.1 Solar Cells . 52 2.7.2 Batteries . 53 2.8 Miscellaneous . 53 Contents v 2.8.1 Lock Motor . 53 2.8.2 Cooling System . 54 2.8.3 Thermometry . 55 2.8.4 Telemetry . 55 3 The Experiments . 57 3.1 Scanning Strategies . 57 3.2 Flight Planning . 59 3.3 In-Flight Diagnostics . 61 3.3.1 Bolometer Biases and Phases . 62 3.3.2 Pointing . 65 3.3.3 Flux Calibration . 65 3.4 Test Flight (2003) . 66 3.4.1 Flight Hardware . 66 3.4.2 Performance . 67 3.5 First Science Flight (2005) . 67 3.5.1 Flight Hardware . 67 3.5.2 Performance . 68 3.5.3 Observations . 70 3.6 Second Science Flight (2006) . 73 3.6.1 Flight Hardware . 73 3.6.2 Performance . 74 3.6.3 Observations . 76 4 Data Processing . 80 4.1 Data Cleaning . 80 4.1.1 Spike Removal and Filter Deconvolution . 81 4.2 Calibration . 83 4.2.1 Time-varying Calibration . 83 4.2.2 Flat-fielding . 83 4.2.3 Absolute Calibration . 85 4.3 Pointing Solution . 86 Contents vi 4.3.1 Gyroscopes . 88 4.3.2 Star Cameras . 88 4.3.3 Integration . ..
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