Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Astronomy

Supervisor

Martin Houde

Abstract

Star formation is a fundamental process in the evolution of the cosmos. Yet given the abundance of stellar constituents, it remains prescient as to why the number of stars is not correspondingly large. If we cannot satisfactorily explain how stars are formed, then many further avenues of research are hindered. This thesis makes claims about one of the foremost theories as to the relative lack of stars, interstellar magnetic fields. These fields have been observationally verified on multiple scales. I will use the most direct method to probe magnetic fields in known star-forming regions, polarization, at millimetre/submillimetre wavelengths. In particular I will focus on the effect that magnetic fields have on the emission produced by rotational molecular transitions. Much of the background behind the study of magnetic fields, and their deduction through submillimetre polarimetry, will be developed in Chapter 1. Here I provide an overview of not only the role that magnetic fields may play in star formation, but also the competing theories of turbulence and magnetohydrodynamic waves. The various manifestations of polarization will also be covered, including polarized molecular transitions. Chapter 2 will look at one of the most well-studied star-forming regions, Orion KL, through observations of a newly discovered water maser transition at 620.701 GHz. Interstellar masers allow different environments to be probed, regions where more complex activity has created a population imbalance between rotational energy levels. The remaining two chapters will present methods and data from the Four-Stokes-Parameter Spectral-Line Polarimeter at the Caltech Submillimeter Observatory. I will look at considerations that must be made when a small map is collected by way of quantifying the amount of instrumental polarization. Spurious polarization signals may pervade the outer edges of the telescope beam, leading to a misrepresentation of the true amount of source polarization. Chapter 3 details the methods involved in removing sidelobes plus the other sources of instrumental polarization, while Chapter 4 goes on to present the actual data to which these techniques have been applied. The data itself is of the molecular transition $^{12}$CO$(J=2\rightarrow1)$, prominent within the protostellar source OMC-2 FIR 4.

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