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Issue A&A
Volume 390, Number 3, August II 2002
Page(s) 829 - 861
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20011755



A&A 390, 829-861 (2002)
DOI: 10.1051/0004-6361:20011755

The Westerbork HI survey of spiral and irregular galaxies

I. HI imaging of late-type dwarf galaxies
R. A. Swaters1, 2, 3, T. S. van Albada1, J. M. van der Hulst1 and R. Sancisi4, 1

1  Kapteyn Astronomical Institute, PO Box 800, 9700 AV Groningen, The Netherlands
2  Dept. of Physics and Astronomy Johns Hopkins University, 3400 N. Charles Str., Baltimore, MD 21218, USA
3  Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
4  Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy

(Received 3 August 2001 / Accepted 6 December 2001)

Abstract
Neutral hydrogen observations with the Westerbork Synthesis Radio Telescope are presented for a sample of 73 late-type dwarf galaxies. These observations are part of the WHISP project (Westerbork $\ion{H}{i}$ Survey of Spiral and Irregular Galaxies). Here we present $\ion{H}{i}$ maps, velocity fields, global profiles and radial surface density profiles of $\ion{H}{i}$, as well as $\ion{H}{i}$ masses, $\ion{H}{i}$ radii and line widths. For the late-type galaxies in our sample, we find that the ratio of $\ion{H}{i}$ extent to optical diameter, defined as 6.4 disk scale lengths, is on average 1.8 $\pm$ 0.8, similar to that seen in spiral galaxies. Most of the dwarf galaxies in this sample are rich in $\ion{H}{i}$ with a typical $M_{\ion{H}{i}}/L_B$ of 1.5. The relative $\ion{H}{i}$ content $M_{\rm\ion{H}{i}}/L_R$ increases towards fainter absolute magnitudes and towards fainter surface brightnesses. Dwarf galaxies with lower average $\ion{H}{i}$ column densities also have lower average optical surface brightnesses. We find that lopsidedness is as common among dwarf galaxies as it is in spiral galaxies. About half of the dwarf galaxies in our sample have asymmetric global profiles, a third has a lopsided $\ion{H}{i}$ distribution, and about half shows signs of kinematic lopsidedness.


Key words: surveys -- galaxies: dwarf -- galaxies: structure

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