Mass-to-light ratios from the fundamental plane of spiral galaxy discs

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Abstract
The best-fitting two-dimensional plane within the three-dimensional space of spiral galaxy disc observables (rotational velocity υrot, central disc surface brightness μ0=-2.5 log I0 and disc scalelength h) has been constructed. Applying the three-dimensional bisector method of regression analysis to a sample of ∼100 spiral galaxy discs that span more than 4 mag arcsec−2 in central disc surface brightness yields (B band) and (R band). Contrary to popular belief, these results suggest that in the B band, the dynamical mass-to-light ratio (within four disc scalelengths) is largely independent of the surface brightness, varying as . Consistent results were obtained when the range of the analysis was truncated by excluding the low-surface-brightness galaxies. Previous claims that M/LBvaries withare shown to be misleading and/or caused by galaxy selection effects – not all low-surface-brightness disc galaxies are dark matter dominated. The situation is, however, different in the near-infrared where LK′∝υ4 and M/LK′ is shown to vary as . Theoretical studies of spiral galaxy discs should therefore not assume a constant M/L ratio within any given passband.
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