Dynamics of Galaxy Interactions

4. Tidal Interactions

Encounter Survey

Initial Conditions. Before colliding, two disk galaxies are rotated about the vertical axis to illustrate the initial conditions (Barnes 1992). Each galaxy contains a thin disk (blue), a central bulge (yellow), and a dark halo (red). One disk lies in the orbit plane, and spins in the same direction that the galaxies circle each other; the other disk is inclined by 71 degrees.

Time Evolution. The galaxies approach each other, tidally interact as they pass each other, and fling out tidal bridges and tails. Subsequently they reach maximum separation, fall back together, and merge. The counter in the upper right shows time in units of 250 million years.

Rotation, t = 1.5. About 125 million years after first passage, the galaxies have developed extended bridges and tails. These are shown to advantage by rotating about the vertical axis as in this video.

Encounter D. Close parabolic encounter of identical bulge/disk/halo galaxies. One disk is inclined by 109 degrees, the other by 180 degrees..

Encounter F. Close parabolic encounter of identical bulge/disk/halo galaxies. One disk is inclined by 71 degrees, the other by 109 degrees.

Encounter D2. Close parabolic encounter of similar bulge/disk/halo galaxies with a three-to-one mass ratio. The small disk is inclined by 71 degrees, the large disk by 109 degrees.

Bars & Spirals

Direct Disk. To show the reaction of the ``direct'' or in-plane disk, this video views this galaxy face-on while representing its partner as a dot (Barnes 1992).

Inclined Disk. Complementing the video above, this one views the inclined disk face-on while representing its partner as a dot.

Tidal Dwarf Galaxies

Dwarf Formation. This sequence shows the formation of a massive bound object in a tidal tail (Barnes & Hernquist 1996). Here stars and gas which wind up in the ``dwarf'' are shown in blue and green, respectively, while other disk and bulge stars are shown in red; halo matter is not shown.

Last modified: June 10, 1997