Dark matter or new physics: A direct comparison among competing explanations of galactic rotation curves

Galactic rotation curves provide some of the strongest evidence for the existence of dark matter at galactic scales [1]. However, several alternative explanations are also able to reproduce the observed rotation curves by modifying Newtonian gravity: these include Modified Newtonian Dynamics [2], conformal gravity [3], and the exponential potential [4,5]. A direct comparison of the predictions of various models is desirable, but challenging due to the differences in the formulation and implementation of these models. In this dissertation, we develop a single program that allows predicted rotation curves for dark matter, MOND, and conformal gravity to be directly compared. Since this program, the Parallel Rotation Curve Simulator (PRoCSi), compares all models by utilizing the same routines for integration, interpolation, density model calculation, and related functions, there are no hidden variables that can arise when the output from two separate programs are compared. This eliminates many possible implementation-dependent variables from the comparison, allowing for a more robust analysis of the physics of the problem. Extensive testing with several independent methods is used to establish the computational correctness of PRoCSi [6,7]. Formal error analysis is also conducted for the complete rotation curve fitting process. The PRoCSi curves for the dark matter pseudo-isothermal halo, Modified Newtonian Dynamics, and conformal gravity are compared to the results of other authors [8,9], and new curves are determined from a detailed study of the available data for a sample of 10 spiral galaxies. Finally, the implications for the future of rotation curve fitting are discussed