Rules of behavior for galactic WARPS

A sample of galaxies is now available for which H I 21 cm line observations allow the development of detailed kinematic models based on concentric, circular rings with adjustable inclinations and orbital velocity. By examining these warped systems in a variety of reference frames, clear empirically determined "rules" for the behavior of galactic warps have emerged. Analysis of 12 galaxies with extended, warped H I disks show the following: 1. The H I layer typically is planar within R_25_, but warping becomes detectable within R_H0_= R_26.5_. Warping within R_H0_ appears consistent with a common (i.e., straight) line of the nodes (LON) measured in the plane defined by the innermost regions of the galaxies. 2. Warps change character at a transition radius near R_H0_. 3. For radii larger than R_H0_, the LON measured in the plane of the inner galaxy advances in the direction of galaxy rotation for successively larger radii. Thus, the nodes lie along leading spirals in this frame of reference. 4. The galaxy kinematics uniquely specify a new reference frame in which there is a common LON for orbits within the transition radius and also a differently oriented straight LON for the gas outside the transition radius. This new reference frame is typically inclined by less than 10^deg^ to the plane of the inner galaxy. The lack of a common LON throughout the entire warped disk argues against models that rely on normal bending modes to maintain warp coherence at all radii. Instead, the emerging picture may require galaxy models with two distinct regimes. Behavior in the outer regime is consistent with models that have the LON regressing most rapidly for orbits that are in closest proximity to the flat, stellar disk. In the inner regime, the disk may be settling into a warped mode.