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The Distribution of Maximum Relative Torques in Disk Galaxies | R. Buta
; E. Laurikainen
; H. Salo
; | Date: |
6 Nov 2003 | Subject: | astro-ph | Affiliation: | University of Alabama, University of Oulu | Abstract: | The maximum ratio of the tangential force to the mean background radial force is a useful quantitative measure of the strength of nonaxisymmetric perturbations in disk galaxies. Here we consider the distribution of this ratio, called Qg, for a statistically well-defined sample of 180 spiral galaxies from the Ohio State University Bright Galaxy Survey and the Two Micron All-Sky Survey. Qg is derived from gravitational potentials inferred from near-infrared images under the assumptions of a constant mass-to-light ratio and an exponential vertical density law. In order to derive the most reliable maximum relative torques, orientation parameters based on blue-light isophotes are used to deproject the galaxies, and the more spherical shapes of bulges are taken into account using two-dimensional decompositions which allow for analytical fits to bulges, disks, and bars. Also, vertical scaleheights hz are derived by scaling the radial scalelengths hR from the two-dimensional decompositions allowing for the type dependence of hR/hz indicated by optical and near-infrared studies of edge-on spiral galaxies. The impact of dark matter is assessed using a "universal rotation curve" parametrization, and is found to be relatively insignificant for our sample. In agreement with a previous study by Block et al. (2002), the distribution of maximum relative gravitational torques is asymmetric towards large values and shows a deficiency of low Qg galaxies. However, due to the above refinements, our distribution shows more low Qg galaxies than Block et al. We also find a significant type-dependence in maximum relative gravitational torques, in the sense that Qg is lower on average in early-type spirals compared to late-type spirals. | Source: | arXiv, astro-ph/0311143 | Services: | Forum | Review | PDF | Favorites |
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