Correlation Statistics of Irregular and Spiral Galaxies Mapped in HI

Abstract

Several measures of galaxy size and mass obtained from the neutral hydrogen mapping of 70 dwarf irregular galaxies presented in Paper I (Hoffman et al. 1996) are compared statistically to those for the set of all available HI-mapped dwarfs and HI-mapped spirals distributed within the same spatial volume to investigate variations in Tully-Fisher relations and in surface densities as functions of galaxy size and luminosity or mass. Some ambiguities due to the ``non-commutativity'' of the correlations among the variables are addressed and linear regressions of logarithms of blue luminosity, HI and optical radii, velocity profile half-width incorporating rotation and random motions, HI mass, and indicative dynamical mass are presented and analyzed. The surface density of HI is almost constant along the sequence of size/mass/luminosity while surface density of blue luminosity increases with galaxy size. For quantities not involving HI we find no evidence for a ``break'' between dwarfs and spirals, but we do find some curvature in velocity vs. radius and in the Tully-Fisher relation. There is an indication for a difference in the correlations involving HI mass or radius between dwarfs alone and spirals alone, in the sense that irregulars have somewhat more HI mass or slightly larger HI radii than spirals at a given blue luminosity, optical radius, or velocity profile width.