The frequency of enhanced star formation in interacting and isolated galaxies

To probe the sensitivity of the star formation rate and extent in galaxies to gravitational encounters, ground based near and mid-infrared and IRAS far-infrared measurements of complete samples of isolated and interacting pairs of galaxies were obtained. The observed infrared properties of the isolated galaxies are used to gauge the magnitude of star formation in galaxies free from external influences, and to define the relationships between morphological type and infrared luminosity. These properties were contrasted with those of the interacting sample to examine the extent to which interactions can enhance or alter the nature of star formation. The mechanisms by which interactions influence activity such as star formation are investigated through correlations of the infrared characteristics with radio and optical measurements, and with morphological and physical parameters such as galaxy types, separations, encounter velocities and interaction types. Limits to the physical extent of the star formation are obtained by comparing the large aperture measurements of IRAS with the small aperture ground based photometry.