Smooth and starburst tidal tails in the gems and goods fields

GEMS and GOODS fields were examined to z similar to 1: 4 for galaxy interactions and mergers. The basic morphologies are familiar: antennae with long tidal tails, tidal dwarfs, and merged cores; M51- type galaxies with disk spirals and tidal arm companions; early- type galaxies with diffuse plumes; equal- mass grazing collisions; and thick J- shaped tails beaded with star formation and double cores. One type is not common locally and is apparently a loose assemblage of smaller galaxies. Photometric measurements were made of the tails and clumps, and physical sizes were determined assuming photometric redshifts. Antennae tails are a factor of similar to 3 smaller in GEMS and GOODS systems compared to local antennae; their disks are a factor of similar to 2 smaller than locally. Collisions among early type galaxies generally show no fine structure in their tails, indicating that stellar debris is usually not unstable. One exception has a 5X10(9) M-circle dot smooth red clump that could be a pure stellar condensation. Most tidal dwarfs are blue and probably form by gravitational instabilities in the gas. One tidal dwarf looks like it existed previously and was incorporated into the arm tip by tidal forces. The star- forming regions in tidal arms are 10 - 1000 times more massive than star complexes in local galaxies, although their separations are about the same. If they all form by gravitational instabilities, then the gaseous velocity dispersions in interacting galaxies have to be larger than in local galaxies by a factor of similar to 5 or more; the gas column densities have to be larger by the square of this factor.