AAS 202nd Meeting, May 2003
Session 40 Galaxies
Poster, Wednesday, May 28, 2003, 10:00am-6:45pm, West Exhibit Hall

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[40.09] A Technique for Separating the Gravitational Torques of Bars and Spirals in Disk Galaxies

R. Buta (U. Alabama), D. L. Block (U. Witwatersrand), J. H. Knapen (U. Hertfordshire)

Near-infrared images are useful for analyzing the stellar backbone of disk galaxies, and in particular can be used to derive gravitational potentials (Quillen, Frogel, and Gonzalez 1994, ApJ, 437, 162). We have shown (Buta and Block 2001, ApJ, 550, 243) that from such potentials, the maximum value of the ratio of the tangential force to the mean radial force in the bar region is an easily derived quantity that can represent the most reliable measure of "bar strength" in disk galaxies. However, such maximum relative torques could also be affected by spirals emanating from the ends of bars. In this poster, we describe a Fourier-based method of separating bars from spirals in near-infrared images, such that the maximum torques due to each of these features alone can be derived. The method takes advantage of the fact that a bar is typically a feature with a relatively fixed position angle, and uses a simple assumption to extrapolate the relative Fourier amplitudes of the bar into the spiral region. We outline the complete procedure for a single, representative example, and summarize the main uncertainties in the technique. We also present the first results of application of the technique to a sample of 17 spiral galaxies, and find that the strongest spirals tend to be associated with strong bars. This work was supported by NSF Grant AST-0205143 to the University of Alabama and the Anglo-American Chairman's Fund, University of the Witwatersrand.

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.