The Ellipticity of the Disks of Spiral Galaxies

The disks of spiral galaxies are generally elliptical rather than circular.The distribution of ellipticities can be fit with a log-normal distribution.For a sample of 12,764 galaxies from the Sloan Digital Sky Survey Data Release1 (SDSS DR1), the distribution of apparent axis ratios in the i band is bestfit by a log-normal distribution of intrinsic ellipticities with ln epsilon =-1.85 +/- 0.89. For a sample of nearly face-on spiral galaxies, analyzed byAndersen and Bershady using both photometric and spectroscopic data, the bestfitting distribution of ellipticities has ln epsilon = -2.29 +/- 1.04. Giventhe small size of the Andersen-Bershady sample, the two distribution are notnecessarily inconsistent. If the ellipticity of the potential were equal tothat of the light distribution of the SDSS DR1 galaxies, it would produce 1.0magnitudes of scatter in the Tully-Fisher relation, greater than is observed.The Andersen-Bershady results, however, are consistent with a scatter as smallas 0.25 magnitudes in the Tully-Fisher relation.Comment: 19 pages, 5 figures; ApJ, accepte