§4 Description of Gallery Figures

We have attempted to present the data in as uniform a manner as possible. To facilitate this, many users contributed the original data in FITS format. The basic data are the integrated intensity maps (zeroth moment), which give the integrated flux (, units of mJy beam km s) at each location. This is usually constructed with the windowing technique to suppress the inclusion of noise (Bosma 1978). The contour levels are given in terms of the surface density, (in units of H atoms per cm), which is obtained from the integrated flux via the equation (see Spitzer 1978, eqn. 3.38 ):

where is the full-width at half-maximum (FWHM) size of the synthesized beam along the major and minor axis, measured in arcseconds, and the gas is assumed to be optically thin.

The contour levels are given in each figure caption, and are usually separated by factors of two. For a small number of systems, it was not possible to derive contour levels.

Spectral line observations also provide line-of-sight velocity information. This information is very informative, but we have decided against its inclusion here, mostly because we had our hands full collecting the integrated intensity maps, but also because such maps beg for a color reproduction. In the future we hope to make the velocity and velocity dispersion maps available, but for the present the readers should refer to the cited literature.

The HI data is shown alongside and contoured upon optical images of each object. When available, we use existing optical CCD data, predominantly donated by the HI observers. Where optical data were not available, we use the Digitized Sky Survey (DSS) ^{image obtained from the Space Telescope Science Institute. We use the second generation survey products when available, prefering the blue plates to the red.}

There is a wealth of information available in the data, and a single format does not do it justice. We have therefore used a combination of layouts. In order to reproduce the figures at as large a scale as possible, the figure captions do not describe the figure layout, which we believe to be reasonably self-evident. The various layouts are described here. The simplest involves a greyscale representation of the optical image on the left, and the optical image with HI column density contours on the right. When the faint optical structure warrants it, we present two representations of the optical data with different transfer functions, in addition to the optical image with HI contours superimposed. Finally, when the complexity of the HI structure warrants it, we also present a greyscale representation of the integrated HI emission. These images show clearly HI minima and maxima, which may be ambiguous in the contour maps. When we do show a greyscale map of the HI, we sometimes include contours. These are most often single contours from the optical data. When there are multiple contours, these are spaced by factors of ten apart. On a few occasions we show HI contours upon the HI greyscales. Since the HI and optical morphologies are so different, it should be obvious what the contours represent.

Positive HI contours are drawn with dark solid lines, and negative contours (e.g., HI absorption against radio continuum sources) are drawn with dashed and/or light lines. Occasionally a larger or smaller field of view (FOV) is also shown, to illustrate either the large-scale HI distribution, or more distant HI-detected companions, or to show details of the inner regions. The smaller FOV is usually indicated by dotted boxes in the larger FOV image.

As mentioned above, the information in the figure captions is kept to a minimum. For the HI data we report the telescope (and array configuration for VLA data), synthesized beam resolution (FWHM), and contour level. For the optical data we report the telescope and filter combination, or simply ``DSS'' when data from the Digital Sky Survey are used, and we give for each image the approximate FOV in arcminutes. There is a section for minimal notes, and finally the reference. Unpublished data is listed as ``[authors], these proceedings'' with a page number. These refer either to contributions presented at the conference and collected in the first part of these proceedings, or to abstracts collected at the end of the Gallery.

In the first panel of each figure we label each galaxy with a catalog designation and the Hubble Type reported in the NASA Extragalactic Database (NED). We also indicate whether NED lists the galaxy with a Seyfert classification. These classifications have not been verified, and should only be used as rough guides. They are included because we find it interesting when galaxies classified as early types are found to have lots of HI, and when galaxies classified as spirals are found to have none or very little. Using NED we have attempted to identify all cataloged galaxies with HI detections, as well as galaxies with known redshifts which place them within the range of the HI observations. Galaxies with their names labeled in parenthesis have redshifts which put them in the foreground or background.