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

School of Mathematics, Sheffield University, Sheffield, S3 7RH, UK

Corresponding author: D.Roscoe@shef.ac.uk

Received: 10 October 2001
Accepted: 24 January 2002

Abstract

In Roscoe ([CITE]), it was described how the modelling of a small sample of optical rotation curves (ORCs) given by Rubin et al. ([CITE]) with the power-law , where where the parameters vary between galaxies, raised the hypothesis that the parameter A (considered in the form ) had a preference for certain discrete values. This specific hypothesis was tested in that paper against a sample of 900 spiral galaxy rotation curves measured by Mathewson et al. ([CITE]), but folded by Persic & Salucci ([CITE]), and was confirmed on this large sample with a conservatively estimated upper bound probability of 10^-7 against it being a chance effect. In this paper, we begin by reviewing the earlier work, and then describe the analyses of three additional samples; the first of these, of 1200+ Southern sky ORCs, was published by Mathewson & Ford ([CITE]), the second, of 497 Northern sky ORCs, is a composite sample provided by kind permission of Giovanelli & Haynes published in the sequence of papers Dale et al. ([CITE], [CITE], [CITE]) and Dale & Uson ([CITE]), whilst the third, of 305 Northern sky ORCs, was published by Courteau ([CITE]). These analyses provide overwhelmingly compelling confirmation of what was already a powerful result. Apart from other considerations, the results lead directly to what can be described as a “second generation of Tully-Fisher methods”. We give a brief discussion of the further implications of the result.