In this paper a study of the neutral hydrogen properties of a sample of 108 galaxies, based on short 21-cm observations with the WSRT, has been presented. The observations, described in Papers I and II, provide one-dimensional information on the kinematics and spatial distribution of the neutral hydrogen along the major axis of each galaxy in the form of a position-velocity (XV) map. The kinematics will be discussed in an accompanying paper (Rhee & Broeils 1996). From these maps a number of H I properties were derived, like H I fluxes and masses, radial H I surface density profiles, and isophotal diameters of the H I discs.
In the first part of this paper these properties were correlated with the optical properties of the underlying galaxies, like luminosities, morphological type and an optical diameter. The main results are:
The second part of this paper described a Principal Component Analysis of the radial H I density distributions of the sample galaxies. We showed that of the variations among surface density profiles can be accounted for by just two principal components. The first, dominant component is clearly linked to the "scale"; it has the same sign at all radii. In other words, the process that is linked to this component works in such a way that if it makes the surface density higher at one point it makes it higher at all other points. The second component is linked to the behaviour of the density profile in the central regions: peak or depression. The third component, which still accounts for of the variation, is most likely responsible for bumps and wiggles in the observed density profiles and could be linked to the presence of H I arms and rings. This could be confirmed by performing PCA to a large sample of galaxies with full two-dimensional synthesis observations of the neutral hydrogen distribution.
© European Southern Observatory (ESO) 1997
Online publication: May 5, 1998