SIMBAD references

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.