The Connection between Galaxy Kinematics and HI Line Widths as Applied to the Distance Scale

This document is fairly old. For more current information, please see my dissertation.

The Tully-Fisher (TF) relation (Tully & Fisher 1977) describes the empirical connection between neutral hydrogen (HI) global line profile widths and the absolute magnitudes of spiral galaxies. TF relations have been used as a powerful tool to calculate distances to galaxies (Jacoby et al. 1992), and therefore play an important role toward solving fundamental problems in Astronomy, such as determination of the Hubble constant (Theureau et al. 1997; Strauss & Willick 1995).

The errors in corrected line-widths are the dominant source of error in the TF-relation (Jacoby et al. 1992; Bothun & Mould 1987). The main cause of errors in corrected line-profile widths arise from several factors, such as low signal-to-noise ratio of the profiles, lack of a standard definition of the line-profile widths and lack of a proper definition of inclination correction. For example:

I am developing a detailed kinematic model of neutral hydrogen in galaxies to simulate real-world HI line profiles of galaxies. In addition to learning about calibration issues mentioned above, the program is being developed with the aim of gaining insight into various other factors that go into the TF relation. The model would be used to create HI line profiles of galaxies based upon the factors we know about the 3-dimensional galaxy velocity fields. For example, the model would incorporate velocity fields, rotation curve shapes, turbulences, density distibution, density waves, warps, high-velocity clouds, etc. Then, the model could be used to study the effect of these parameters on the line profiles of galaxies.

The model is being developed in Python. As of now, I have a basic 3-dimensional galaxy model ready, which can be used to create line-profiles of galaxies with different velocity distributions.

The data for the model (rotation curves, line profiles, etc.) comes from existing literature and observations of galaxies using the Green Bank Telescope and the Giant Meterwave Radio Telescope.

Future work involves extending this model to incorporate other parameters mentioned, and then fine-tuning the model so as to predict the line-profiles of various galaxies.


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Last modified: Thu, 01 Apr 2010 12:55:47 -0400