HI profile distances and the Hubble constant

Since the discovery of the expansion law of the universe the search has been on for a standard candle visible to distances at which redshifts are dominantly cosmological. A dozen or so extragalactic distance indicators have been considered but all contain factors which could cause systematic errors. The recently proposed correlation between intrinsic luminosity or diameter and a distance-independent parameter, the global HI line profile width, offers hope for an improved method. If the intrinsic errors in this method are as small as they appear to be with the present data, out to 100 Mpc or so, this could be the best distance indicator available. Not only should we get accurate distances to individual galaxies but, since the observations required are straightforward, the method can be applied to hundreds, potentially thousands, of galaxies. The Hubble constant should be well constrained and it should be possible to study detailed deviations from the Hubble flow. The new approach is examined and applied to the Virgo cluster. (U.K.)