Lifetime of merger features of equal-mass disk mergers

Context. Detecting post-merger features of merger remnants is highly dependent on the depth of observation images. However, there has not been much discussion of how long the post-merger features are visible under different observational conditions. Aims. We investigate a merger-feature time useful for understanding the morphological transformation of galaxy mergers via numerical simulations. Methods. We used N-body/hydrodynamic simulations, including gas cooling, star formation, and supernova feedback. We ran a set of simulations with various initial orbital configurations and with progenitor galaxies having different morphological properties mainly for equal-mass mergers. As reference models, we ran additional simulations for non-equal mass mergers and a merger in a large halo potential. Mock images using the SDSS r band were synthesized to estimate a merger-feature time and compare it between the merger simulations. Results. The mock images suggest that the post-merger features involve a small fraction of stars, and the merger-feature time depends on galaxy interactions. In an isolated environment, the merger-feature time is, on average, similar to 2 times the final coalescence time for a shallow surface bright limit of 25 mag arcsec(-2). For a deeper surface brightness limit of 28 mag arcsec(-2), however, the merger-feature time is a factor of two longer, which is why the detection of post-merger features using shallow surveys has been difficult. Tidal force of a cluster potential is effective in stripping post-merger features out and reduces the merger-feature time.