Morphology of Galaxy Mergers at Intermediate Redshift

Abstract

Using a combination of numerical simulation and synthesized Hubble Space Telescope Wide Field Camera 2 (HST WFC2) images, we follow the detectability of morphological signatures of disk galaxy mergers at intermediate redshifts z=0.4 and z=1.0. Rapid evolution in the surface brightness of tidal tails makes their use as an interaction signature limited; long tidal tails will only be detectable relatively early in the encounter, before the galaxies actually merge. Violent relaxation rapidly smooths isophotal irregularities after the galaxies merge, leaving the very low surface brightness tidal debris surrounding the remnant as the only sign of peculiarity after a few hundred Myr. This debris becomes indistinguishable from the main body of the remnant after 0.5 (z=1.0) to 1 (z=0.4) Gyr, leaving a morphologically normal elliptical galaxy behind. Using WFC1, all signatures become undetectable almost immediately once the galaxies merge, due to the aberrated PSF. We interpret these results in light of recent HST programs investigating the nature of starburst and E+A galaxies in moderate redshift clusters.