Multi-Waveband Observations of Colliding Galaxies

Abstract

Colliding galaxies represent a major challenge to both theorists and observers because of the large variety of phenomina which are expected to come into play during the interaction. Strong gravitational fluctuations may drive non-linear waves and instabilities throughout the stars and gas leading to enhanced star formation, nuclear activity and ultimately a mixing of the morphological components of the original galaxies. One relatively uncomplicated class of colliding galaxy where stellar waves play an important role in star formation are “ring” galaxies. Ring galaxies are probably formed when a companion galaxy passes through the centre of a disk system driving circular waves through the disk (Lynds and Toomre 1976, Toomre 1978, Struck-Marcell 1990). Off-centre collisions can generate non-circular waves and can be loosely described as banana-shaped although they may exhibit more complex forms as the waves expand into the disk (See also Struck-Marcell; this volume). The propagation of such stellar and gaseous waves through the disk leads to enhanced star formation (e.g. Appleton and Struck-Marcell 1987a; Jeske 1986) and provides a unique probe of the response of the ISM to a propagating wave (See Appleton and Struck-Marcell 1987b).