To get the characteristics of the gaseous stream from S galaxy numerical solution of equations of test particle motion were carried out (Sotnikova 1988a). Many sets of initial conditions were used and two different cases were considered. (i) The direction of spiral galaxy spin and that of orbital momentum are the same. (ii) These directions are opposite. The main results of the computations are: 1. In the case (i) the time scale of stream formation is much smaller than in case (ii). For example, in the last case the test particle has stayed on its circular orbit in S galaxy during the period of revolution of the whole system (~3.108 years). 2. In case (i) during one revolution of the binary system the stream evolves to quasi steady state (Figure 2). The S galaxy loses about 0.5% of the total amount of gas per period of the disk revolution (~108 years). Mean values of the parameters for systems with interacting S-E galaxies from Karachentsev's list (1987) are: rsE = 34 kpc, Ms ISE = (2 1011M. The corresponding cloud transfer rate is Ṁ 0.3)M。 year-1 provided the total mass of gas is about 0.1 Mstars' gas 3) 2 in the galaxy Figure 2. The number of test particles N (the units are arbitrary) lost by spiral galaxy, at the time t = t/2.1. 108 years (rSE = 34 kpc, Ms = 2 • 1011 M。), q = I, Rs/rSE = 0.35, RE/ISE = 0.35. CONCLUSIONS ~ 109 years) a In the course of S-E pair evolution (tev significant amount of gas may be transferred to E galaxy (M tev 108 gas multiple systems. One may mention also that the presence of emission lines in spectra of many E components of close S-E pairs (25%) may be caused by gas gained by E galaxies due to the tidal interaction with S galaxies. REFERENCES Bottinelli, L., and Gougenheim, L. 1978, Astron. Astrophys., 76, 176. Demin, V. V., Zasov, A. V., Dibaj, Eh. A., and Tomov, A. N. 1984, Astron. Zh., 61, 625. Faber, S. M., Gallagher, J. S. 1979, Annu. Rev. Astron. Astrophys., 17, 135. van Gorkom, J. H., Knapp, G. R., Raimond, E., Faber, S. M., Gallagher, J. S. 1986, Astron. J., 91, 791. Karachentsev, I. D. USSR, 248 pp. 1987, Dvojnye Galaktiki, Nauka, Moscow, Smirnov, M. A., and Komberg, B. V. 1980, Astrofizika, 16, 431. Sotnikova, N. Ya. 1986, Astrifizika, 25, 139. Sotnikova, N. Ya. 1988a, Astrofizika, 28, 495. Sotnikova, N. Ya. 1988b, Ph.D. Thesis, Leningrad University, Leningrad. Varnas, S. R., Bertola, F., Galleta, G. 1987, Astrophys. J.,. 313, 69. 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 interacting 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/arcsec2) 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. |