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For refcode 1989AJ.....97.1566K:
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1989AJ.....97.1566K THIN EDGE-ON GALAXIES AS A TOOL FOR THE INVESTIGATION OF LARGE-SCALE STREAMING MOTIONS IN THE UNIVERSE IGOR KARACHENTSEV Special Astrophysical Observatory, USSR Academy of Sciences, St. Zelenchukskaya, Stavropolskij Kraj 857140, USSR and Arecibo Observatory, National Astronomy and Ionosphere Center, Box 995, Arecibo, Puerto Rico 00613 Received 7 November 1988; revised 23 January 1989 ABSTRACT When the Tully-Fisher relation is used to determine the distances to galaxies, edge-on spiral galaxies are usually excluded, because of the large fluctuations introduced by the internal extinction in these objects. Based on a sample of 324 galaxies observed at Arecibo, we demonstrate that this effect is less significant than has been usually assumed. Moreover, we show that the scatter of galaxies in the TF diagram ("H I profile width-linear diameter") steadily decreases, when the axial ratio a/b increases. For the flattest and the most inclined galaxies (a/b > 7), the scatter in the TF diagram yields a root-mean-square error in distance estimates of 10^+/- 0-09^. Not only the H I linewidths but also the H I fluxes of flat galaxies are strongly correlated with their optical diameters: at a given flux, the rms scatter in diameter is only 10^+/- 0.03^. At present, the effect of "latent parameters" on the TF diagram cannot be properly estimated, due to the lack of reliable photometric data for a representative sample of flat galaxies. Using the photometric data of Watanabe (1983), we have obtained the rms deviation of 10 +/- ^0.048^ with respect to the relation W_H I_ proportional to h^0.5^ I^0.5^), which surprisingly resembles a similar relation, {sigma}_{nu}_, proportional to R^0.72^_e_ I^0.65^_e_, that has been derived for E galaxies (Hoessel et al. 1987). We have applied the criterion a/b > 7 to select 1547 flat galaxies from the UGC, ESO(B), and MCG catalogs. Their distribution over the sky has essentially less contrast than in the case of other galaxies and, in particular, it does not show a signature of the Local Supercluster. Here, we give a brief description of the new Catalogue or Flat Galaxies (FGC), currently in preparation, which will cover the whole sky with an effective depth z_e_~0.05 and will contain about 8000 objects. The catalog has several characteristics that make it particularly suitable for the studies of large-scale streaming motions in the universe: (i) the catalog members are disklike, flat galaxies with a simple structure; (ii) the selection criterion used (a/b > 7) makes the sample morphologically homogeneous; (iii) the 21 cm line detection rate of these galaxies is nearly 100%; and (iv) the flat galaxies avoid volumes occupied by groups and clusters so that their structure remains undisturbed and they are not affected by large virial motions.
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