ABSTRACT

It has been claimed that spherically symmetric, isothermal (ρ ∼ r-2) halos of invisible material surround certain galaxies and extend to between ≈ 40 kpc (Rubin et al. 1985) and ≈ 1 Mpc (Charlton and Salpeter 1991) from their centers. In this work in progress we consider the tidal effects due to the presence of such halos in binary galaxies. Having investigated the predicted frequency of tidal distortions we then compare with binary galaxy surveys to search for evidence of these effects.

TIDAL RADIUS

A tidal radius was calculated based upon a simplified model of a binary galaxy system. Each member of the system is identical and in a circular orbit about the system's center of mass. The dark matter halos extend to the point where they just begin to overlap and the visible disk of each galaxy, despite rotating on its axis, is taken to be approximately spherically symmetric. Furthermore, the rotational angular momentum vector of the material contained in each visible disk is taken to be parallel to the orbital angular momentum vector for the entire system. This information was used to determine the radial equation of motion for a test particle located at the outer edge of either visible disk and from this equation the tidal radius is obtained (≈ 40 kpc). The tidal radius is the separation between members of the binary system at which the test particle just begins to leave the visible disk.