7 Summary

We have reported the results of an H I 21-cm line survey of a sample of 472, late-type, edge-on spiral galaxies. Our targets were primarily selected from the Flat Galaxy Catalogue (FGC) of Karachentsev et al. (1993), and thus represent a sample of highly flattened, pure disk galaxies. Most of the galaxies observed have apparent disk axial ratios $a/b\ge7$ and little or no bulge component. Our sample was primarily composed of Scd and later spirals, with an emphasis on the largest angular size and lowest optical surface brightness galaxies in the FGC. Our survey covered objects over the entire sky north of $\delta=-44.5^{\circ}$.

Approximately 50% of the targets (232 galaxies) were detected within $V_{\rm h}<10\,000$ km s^-1; 78% of these galaxies had no previously reported redshifts and H I parameter measurements. Our detection rate should be regarded as a strict lower limit for the detectability of late-type pure disk galaxies within the nearby universe, since due to telescope scheduling limitations, the spectral noise level was not uniform for each target, and our velocity coverage for many of the undetected targets was incomplete. The high detection rate of our survey in spite of these limitations underscores that small, gas-rich, pure disk spirals are an extremely common constituent of the nearby universe. Our survey has added roughly 70 previously unrecognized gas-rich members to the Local Supercluster alone. Even if they do not contribute appreciably to the local luminosity density of the universe, any robust galaxy formation paradigm must account for the abundance of these small, bulge-free disks in the present epoch.

Among the targets detected in our present survey, non-dwarf companions appear to be rare. Only 10 targets are believed to have neighbors at similar radial velocities within a projected radius of 18' (i.e., $\sim 1.5$ times the FWHP telescope beam radius). Only 4 of these 10 galaxies are "superthin'' (i.e. have axial ratios $a/b\ge$ 10), and 3 of those 4 galaxies show signs of optical disturbances in their disks. Our data appear to be consistent with the notion that highly flattened, pure disk galaxies tend to be isolated galaxies, and that the presence of neighbors tends to thicken their disks and transform their disk morphologies. The data we have presented here, together with the complementary database of Giovanelli et al. (1997) should allow a more detailed investigation of the 3-D spatial distribution of pure disk galaxies in the local universe, as well a wide variety of studies related to the properties of this common class of nearby galaxy.

Acknowledgements

LDM gratefully acknowledges the partial financial support provided by a Grant-in-Aid of Research from $\Sigma\Xi$, the Scientific Research Society. We thank our referee for alerting us to the availability of the new Revised FGC. The Nançay Radio Observatory is the Unité Scientifique Nançay of the Observatoire de Paris and is associated with the French Centre National de Recherche Scientifique (CNRS) as the Unité de Service et de Recherche (USR), No. B704. The Observatory also gratefully acknowledges the financial support of the Région Centre in France. This research made use of: the NASA/IPAC Extragalactic Database (NED) operated by JPL under contract with NASA; the Lyon-Meudon Extragalactic Database (LEDA), www-obs.univ-lyon1.fr; and the Digitized Sky Surveys (DSS), which were produced at the Space Telescope Science Institute under U.S. Government grant NAG W-2166.