The H I content of spirals .1. Field galaxy H I mass functions and H I mass-optical size regressions

A standard parametric maximum likelihood technique is used to determine both the probability distribution over total H I mass, M(H I), and the regression of this quantity on the linear optical diameter, D-0, for field giant spirals (Sa-Sc) from a complete H I flux-limited data set of these objects. This sample is extracted from a subset of the optical magnitude-limited Catalog of Galaxies and Clusters of Galaxies comprised of galaxies observed in the 21 cm H I line and located in the lowest density environments of the Pisces-Perseus supercluster region bounded by 22(h) less than or equal to R.A. less than or equal to 3(h), 0 degrees less than or equal to decl. less than or equal to 40 degrees. Gaussian and Schechter parameterizations of the H I mass function are explored. We find that the available data are equally well described by both models and that the different morphological classes of giant spirals have H I mass functions that, in general, agree well within the errors. The largest discrepancy corresponds to the Sb-type systems that exhibit a deficit of low H I-mass objects relative to the other types. Using a straightforward generalization of the Gaussian model, we have also investigated the linear dependence of M(H I) on D-0. We confirm that the H I content of spirals is much better predicted by the size of their optical disks than by their morphological types alone. The inferred correlations imply a considerable decrease of the ratio M(H I)/D-0(2) with increasing galaxy size for types earlier than Sc.