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Astron. Astrophys. 324, 877-887

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Short 21-cm WSRT observations of spiral and irregular galaxies

H I properties

A.H. Broeils1 and M.-H. Rhee2

1Stockholm Observatory, S-13336 Saltsjöbaden, Sweden
2Kapteyn Astronomical Institute, Postbus 800, 9700 AV Groningen, The Netherlands

Received 13 May 1996 / Accepted 15 January 1997


We present the analysis of neutral hydrogen properties of 108 galaxies, based on short 21-cm observations with the Westerbork Synthesis Radio Telescope (WSRT). The results of two H I surveys are analysed to investigate the existence of relations between optical and H I properties, like diameters, hydrogen masses and average surface densities. For all galaxies in our sample we find that the H I diameter, defined at a surface density level of FORMULA , is larger than the optical diameter, defined at the FORMULA mag arcsec-2 isophotal level. The H I-to-optical-diameter ratio does not depend on morphological type or luminosity. The strongest, physically meaningful, correlation for the sample of 108 galaxies is the one between log MHI and log DHI, with a slope of 2. This implies that the H I surface density averaged over the whole H I disc is constant from galaxy to galaxy, independent of luminosity or type. The radial H I surface density profiles are studied using the technique of principal component analysis. We find that about 81% of the variation in the density profiles of galaxies can be explained by two dimensions. The most dominant component can be related to "scale" and the second principal component accounts for the variance in the behaviour of the radial profile in the central parts of galaxies (i.e. "peak or depression") . The third component accounts for 7% of the variation and is most likely responsible for bumps and wiggles in the observed density profiles.

Key words: galaxies: fundamental parameters - galaxies: structure - galaxies: kinematics and dynamics - galaxies: spiral - radio lines: galaxies

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© European Southern Observatory (ESO) 1997