The galaxies in this figure were found in a strip of sky surveyed in the 21 cm line of neutral hydrogen (HI). All galaxies are shown to the same linear scale (adjusted for their distance), and with the same photographic "stretch." The galaxies on the left were discovered in the survey and are given a running number from the discovery list, while the objects on the right were previously cataloged optically and are given their common name and number. The objects are shown in order of increasing hydrogen mass from top to bottom of the figure. Their HI spectral lines are shown in the bottom of the panels, and the HI mass in billions of solar masses and redshift velocities are listed after the source name.
There is a great deal of information to be gleaned from these data. The optically cataloged objects tend to have a higher optical surface brightness, and larger physical size than the objects found via the HI search. The lowest mass HI dwarf has no clear optical counterpart. Conversely, some of the objects that are optically brightest have no detectable HI. Further analysis of the source counts suggests that the low-mass sources may represent a major repository of the HI in the universe.
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Last Update: 11/20/1996