paper

Discrete dynamical classes for galaxy discs and the implication of a second generation of Tully-Fisher methods

arXiv:astro-ph/0107300 · doi:10.1051/0004-6361:20020166

Abstract

We consider the four large optical rotation curve samples of Mathewson, Ford & Buchhorn (900 ORCs), Mathewson & Ford (1200 ORCs), Dale, Giovanelli, Haynes et al (494 ORCs) and Courteau (300 ORCs). We show how it is possible to partition any given ORC into two distinct dynamical regions - an interior region and an exterior region. Each of the samples considered is partitioned in this way, so that we are able to consider the dynamics on the exterior parts of the ORCs for each of the samples. This technique was originaly introduced by Roscoe astro-ph/0107305. We then find that the dynamics in the exterior part of spiral discs fall into one of four sharply defined classes. Taking account of the various correlations which exist between luminosity properties and dynamical properties of discs, our final phenomonological conclusion is that spiral discs in the samples considered appear constrained to occupy one of four distinct planes, F(M,S,a) = k0, k1, k2, k3, where M = absolute magnitude, S = surface brightness, "a" is a parameter computed directly from each ORC and k0, k1, k2, k3 are well defined numerical constants. These results are statistically supported at the level of virtual certainty. We suggest three possible mechanisms for this phenomonology. The overall analysis implies the existence of a second generation of Tully-Fisher methods in which the standard TF relation is augmented with a second relation defining where on an ORC the linewidth should be measured.

22 pages, 17 figures, to appear in A&A 2002. Expanded with an additional large sample analysed, and implications for extended Tully-Fisher methods included

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