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Probing Interstellar Grain Alignment with Balloon-borne Submillimeter Observations

Natalie Gandilo

Doctor of Philosophy 2015
Graduate Department of Astronomy and Astrophysics, University of Toronto

The role that magnetic fields play in regulating star formation is one of the outstanding issues in star formation theory. Magnetic fields in star-forming clouds in our galaxy can be observed by tracing the polarized emission from interstellar dust grains. However the mechanism by which the dust grains align with the magnetic fields is not fully understood. Grain alignment theories (e.g. radiative alignment torques) make predictions for the observed spectrum of the polarized emission, so observations at multiple wavelengths can be used to test these theories.

The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLASTPol) observes polarized dust at 250um, 350um and 500um while suspended from a balloon in the stratosphere above Antarctica. BLASTPol maps the dust polarization signal over entire molecular clouds, with enough angular resolution to trace the cloud sub-structures and protostellar cores. BLASTPol uses an attitude reconstruction system consisting of multiple sensors, including star cameras, sun sensors and rate gyroscopes. This system allows BLASTPol to point in-flight at specific regions on the sky, and allows the telescope's attitude to be reconstructed post-flight. A similar system was built for SPIDER, a balloon-borne telescope that observes the polarization of the CMB.

The analysis pipeline used to produce science maps is discussed, and science results are presented from BLASTPol's 2012 observations of the Vela C molecular cloud. The polarization spectrum shows a minimum at 350um, similar to the measurements of previous experiments observing other molecular clouds. No strong correlation is seen between the shape of the polarization spectrum and either the temperature or density of the dust. Analysis of the maps is ongoing, and future work will focus on the diffuse dust in the cloud, which is more suitable to compare with dust models.

Reproduced with permission. library@astro.utoronto.ca
August 11, 2015