Flat Edge-On Galaxies and Large-Scale Streamings
When the Tully-Fisher (T-F) relation is used to determine the distances to galaxies, the edge-on, spiral galaxies are usually excluded, due to large fluctuations of the observed extinction in these objects. Based on a sample of 324 galaxies observed at Arecibo, we demonstrate that this effect is less significant than it has been usually assumed. Moreover, we show that the scatter of galaxies in the T-F diagram (“H I profile width versus 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 T-F diagram corresponds to the mean square error in distance estimates of 10±0.09. Not only the H I line widths, but also the H I fluxes of flat galaxies are strongly correlated with their optical diameters: at a given flux, the r.m.s. scatter in diameter is only 10±0.03.