Discrete Components in the Radial Velocities of 83 ScI Galaxies: Examining the Accuracy of Tully-Fisher Distances

Abstract

Our previous analyses of the redshifts and distances of galaxies included 55 spiral galaxies and 36 Type Ia Supernovae galaxies in three separate groups. All groups showed evidence that their radial velocities contain the same discrete velocity components that are predicted from the early work of Tifft. Here we examine another new source sample containing 83 ScI galaxies. When B-band distances are used, we find clear evidence that the discrete velocities defined by Tifft's most common velocity period are present in the radial velocities of these galaxies. Assuming this is true, we are then able to use the visibility, or ease of detection, of the discrete components as an indication of the distance accuracy of the galaxies, comparing B- and I-band distances, galaxy inclination ranges, and galaxy rotation velocity ranges. We find (a), that, contrary to expectation, B-band distances for these sources are considerably more accurate than I-band, (b), that the distance accuracy varies with galaxy inclination, as expected, with the most consistent distances obtained for inclinations between 48 and 65 degrees, and (c), that distances are probably more accurate for small rotation velocities. With these results for the 83 ScI galaxies, discrete velocity components have now been detected in all 174 galaxies examined.