2003/11/06 by R. Buta, E. Laurikainen, H. Salo · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Galaxies: Formation, Evolution, Phenomena #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/379962
Accepted for publication in the Astronomical Journal, January 2004 issue (Latex, 39 pages + 17 figures, uses aastex.cls)
arxiv created 2003/11/06 · openalex publication_date 2004/01/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
The maximum value of the ratio of the tangential force to the mean background radial force is a useful quantitative measure of the strength of nonaxisymmetric perturbations in disk galaxies. Here we consider the distribution of this ratio, called Q g , for a statistically well-defined sample of 180 spiral galaxies from the Ohio State University Bright Galaxy Survey and the Two Micron All Sky Survey. The ratio Q g can be interpreted as the maximum gravitational torque per unit mass per unit square of the circular speed and is derived from gravitational potentials inferred from near-infrared images under the assumptions of a constant mass-to-light ratio and an exponential vertical density law. In order to derive the most reliable maximum relative torques, orientation parameters based on blue-light isophotes are used to deproject the galaxies, and the more spherical shapes of bulges are taken into account using two-dimensional decompositions that allow for analytical fits to bulges, disks, and bars. Also, vertical scale heights h z are derived by scaling the radial scale lengths h R from the two-dimensional decompositions, allowing for the type dependence of h R / h z indicated by optical and near-infrared studies of edge-on spiral galaxies. The impact of dark matter is assessed using a "universal rotation curve" parameterization and is found to be relatively insignificant for our sample. In agreement with a previous study by Block et al., the distribution of maximum relative gravitational torques is asymmetric toward large values and shows a deficiency of low- Q g galaxies. However, because of the above refinements, our distribution shows more low- Q g galaxies than that of Block et al. We also find a significant type dependence in maximum relative gravitational torques, in the sense that Q g is lower on average in early-type spirals than in late-type spirals. The effect persists even when the sample is separated into bar-dominated and spiral-dominated subsamples and also when near-infrared types are used, as opposed to optical types.