OBSERVATIONS AND MODELS OF STAR FORMATION IN THE TIDAL FEATURES OF INTERACTING GALAXIES John F. Wallin Space Science Division, Naval Research Laboratory James M. Schombert Dept. of Astronomy, Univ. of Michigan Curtis Struck-Marcell Astronomy Program, Dept. of Physics, Iowa State University ABSTRACT Multi-color surface photometry (BVri) is presented for the tidal features in a sample of in- teracting galaxies. Large color variations are found between the morphological components and within the individual components. The blue colors in the primary and the tidal features are most dramatic in B-V, and not in V- i indicating that star formation instead of metallicity or age dominates the colors. Color variations between components is larger in systems shortly after interaction begins and diminishes to a very low level in systems which are merged. Photometric models for interacting systems are presented which suggest that a weak burst of star formation in the tidal features could cause the observed color distributions. Dynamical models indicate that compression occurs during the development of tidal features causing an increase in the local density by a factor of between 1.5 and 5. Assuming this density increase can be related to the star formation rate by a Schmidt law, the density increases observed in the dynamical models may be responsible for the variations in color seen in some of the interacting systems. Limitations of the dynamical models are also discussed. INTRODUCTION The IRAS mission has provided evidence that interaction can in some cases lead to enhanced rates of star formation in the disks of interacting galaxies (Larson and Tinsley 1978, Soifer et. al. 1987) Interaction has also been linked to nuclear activity in some studies (Hummel 1981, Bushouse 1986, Keel et al. 1985). In this paper, I wish to focus on the tidal features of interacting galaxies Because the surface brightness is fairly low (mag/arcsec 2 ) in these features, the rate of star formation cannot be considered large when compared to the huge bursts at the centers of some galaxies (i.e. Arp 220). However recent photometric results by Schombert, Wallin, and Struck-Marcell (1990) suggest that the rate of star formation in some tidal features must have increased during the interaction which formed them. 727 https://doi.org/10.1017/S0252921100005881 Downloaded from https://www.cambridge.org/core. IP address: 34.228.24.229, on 09 Jun 2020 at 11:29:26, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.