A MULTICOLOR PHOTOMETRIC-STUDY OF THE TIDAL FEATURES IN INTERACTING GALAXIES

Four-color surface photometry (BVri) is presented for low-surface-brightness tidal features in interacting galaxies. Objects were selected on the basis of visual morphology including a cross section of tails, bridges, plumes, shells, and extended envelopes. Intensity cross sections and surface brightness suggests that plumes are face-on or near face-on sheets; tails and bridges are more nearly one-dimensional, linear figures. In many cases the colors of tidal features are similar to the outer regions of the primary galaxies, confirming the stripping origin hypothesis. However, large color variations are found among the morphological components within most systems, and within individual components. Blue colors in primaries and tidal features are most dramatic in B - V, not V - i indicating that star formation, not metallicity or age, is the dominant component. There is clear evidence in our sample of a correlation between the magnitude of the color variation and the time since the beginning of the interaction as determined by the development of the tidal features. The color variations are largest a short time after the beginning of the interaction, and they diminish to a very low level in merged systems. This correlation provides an alternate estimator of interaction age in systems with ambiguous morphologies, and another constraint to aid in understanding the nature of star formation in interacting systems. On average, 25% of a system's luminosity is tied to tidal features for, although low in surface brightness, their projected area is large.