3 The adopted measure of folding quality

Figure 2:
Comparison of MFB and PS solutions.
The vertical lines in both diagrams indicate the positions of the A, B, C, D
and E peaks in the PS solution |

Figure 2 (left) shows the distribution for the MFB solution (that is, when the rotation curves are folded using MFB's optical centre and their estimate of ), whilst Fig. 2 (right) shows the corresponding distribution for the PS solution. A comparison shows that the peaks labelled B, C and D in the MFB solution are reproduced - enhanced and with much reduced noise - in the PS solution. Since the MFB solutions were determined directly from observational estimates of optical centres and systematic redshifts whilst the PS solutions were determined using a "by-eye'' folding process without any reference to an underlying power-law structure (and hence without reference to any distribution), then the foregoing comparison strongly suggests that the B, C, D peak structure reflects objective physical qualities in the underlying distribution of rotation curves. This conclusion was reached independently (with the addition of the A and E peaks), supported by very strong statistics, in Roscoe 1999B.

For these reasons, the distribution is adopted here as a suitable statistical representation of a folding solution over a large number of rotation curves.

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