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In Search of an Imprint of Magnetization in the Balloon-borne Observations of the Polarized Dust Emission from Molecular Clouds

Juan Diego Soler

Doctor of Philosophy 2013
Graduate Department of Astronomy and Astrophysics, University of Toronto

The observation of the polarization of thermal emission from dust grains is a key method in the study of the role of the magnetic fields in the star formation process. This dissertation introduces BLASTPol, a submillimeter telescope for polarization designed for mapping dust polarization in scales ranging from pre-stellar cores to sections of molecular clouds and the Histogram of Relative Orientations (HRO), a new statistical tool for the analysis of the polarization maps.

The observations of BLASTPol were possible thanks to a novel light-weight carbon fiber sunshield structure and the detailed thermal modeling of the balloon-borne platform. The carbon fiber structure is based on the construction technique developed for the Spider gondola which integrates detailed Finite Element Analysis with the use of composite materials and adhesive joints. The thermal model uses 3D Computer Assisted Design allowing unprecedented control of the sun avoidance limits and detailed modeling of the gondola components.

BLASTPol made observations of the Lupus I and Vela C molecular clouds, the Carina Nebula, and the Puppis Cloud Complex in two balloon-borne flights over Antarctica in 2010 and 2012. The construction of polarization maps from the BLASTPol10 observations was affected by multiple pathologies in the data. However, the preliminary maps indicate the need of a statistical tool which allows relating these observations to magnetohydrodynamics (MHD) simulations motivating the development of HRO. Most of the problems in the BLASTPol10 data were successfully addressed in BLASTPol12 and the construction of polarization maps of the observed regions is currently in progress.

The HRO is a statistical tool which assesses the relative orientation between the magnetic field and the density structures. This tool was characterized by using simulated molecular clouds with different magnetization indicating that: 1. There is an imprint of the magnetization level in the relative orientation of the projected magnetic field with respect to the column density structure. 2. This imprint of magnetization can be used to complement the current estimates of magnetic field strength provided by the Chandrasekhar-Fermi method. HRO establishes a direct link with MHD simulations providing a common tool for the analysis of polarization maps from BLASTPol.

Reproduced with permission. library@astro.utoronto.ca
August 18, 2013