The Connection Between Galaxy Kinematics and Hi Line Widths as Applied to the Distance Scale

I have created a 3-dimensional model of neutral hydrogen (Hi) in disk galaxies, in order to better understand galaxy kinematics and the Tully-Fisher (tf) relationship. The model uses data from existing observations of galaxies (aperture synthesis and single-dish) to calculate some of their observed properties, such as single-dish line profiles, channel maps, and position-velocity diagrams. These can then be compared with the actual observations to study the differences between them. The effect of changing various galaxy parameters (such as inclination, and turbulent motion) on these quantities can then be studied. The model can also be used to study the effect of the parameters and commonly used corrections on the tf relation, such as turbulent motion correction and instrumental correction. Using the model, I have found that the the most commonly used turbulent motion corrections introduce a bias in the corrected line widths, particularly for galaxies with smaller rotation velocities. This can introduce a bias in the slope of the tf relation. Also, from the simulation, some galaxies show the presence of points on their line profiles where their HI line widths are independent of the turbulent motions. If such a point exists for all galaxies, then the determination of line widths at those points will require little or no correction due to turbulent motion effects, and that width can be used in the tf relation instead of the commonly used line widths.