The Ellipticity of the Disks of Spiral Galaxies

Author

Ryden, Barbara S.

Abstract

The disks of spiral galaxies are generally elliptical rather than circular. The distribution of ellipticities can be fitted with a lognormal distribution. For a sample of 12,764 galaxies from the Sloan Digital Sky Survey Data Release 1 (SDSS DR1), the distribution of apparent axis ratios in the i band is best fit by a lognormal distribution of intrinsic ellipticities with \({\rm ln} \epsilon = -1.85 \pm 0.89\). For a sample of nearly face-on spiral galaxies analyzed by Andersen & Bershady using both photometric and spectroscopic data, the best-fitting distribution of ellipticities has \({\rm ln} \epsilon = -2.29 \pm 1.04\). Given the small size of the Andersen & Bershady sample, the two distributions are not necessarily inconsistent with each other. If the ellipticity of the potential were equal to that of the light distribution of the SDSS DR1 galaxies, it would produce 1.0 mag of scatter in the Tully-Fisher relation, greater than is observed. The Andersen & Bershady results, however, are consistent with a scatter as small as 0.25 mag in the Tully-Fisher relation.

Publication

The Astrophysical Journal, Volume 601, Issue 1, pp. 214-220.

Pubdate

January 2004

DOI

10.1086/380437

arXiv

astro-ph/0310097

Bibcode

2004ApJ…601..214R

Keywords

Galaxies: Fundamental Parameters; Galaxies: Photometry; Galaxies: Spiral; Astrophysics

Figures

../../_images/ryden_2004_fig_1.svg

Ryden (2004), Fig. 1

Histogram: Distribution of axis ratio \(q_{\rm am}\), using adaptive moments in the i band, for exponential galaxies in the SDSS DR1. Points with error bars: Best-fitting model, assuming a Gaussian distribution of disk thickness and a lognormal distribution of intrinsic disk ellipticity. The best-fitting model has thickness \(\gamma = 0.222 \pm 0.057\) and ellipticity \(\log\epsilon = -1.85 \pm 0.89\).

Source: sources/ryden_2004/fig_1.py

Ryden (2004), Fig. 1 reproduced by skypy.galaxy.ellipticity.ryden04(). The selection follows everything specified in Section 2 but returns 12,953 galaxies in the i-band instead of the quoted 12,764 galaxies in the paper.