Lifetime of merger features of equal-mass disk mergers

¹ Department of Astronomy and Yonsei University Observatory, Yonsei University, 120-749 Seoul, Republic of Korea
e-mail: yi@yonsei.ac.kr
² Institut d’Astrophysique de Paris (UMR 7095: CNRS & UPMC), 98 bis Bd Arago, 75014 Paris, France

Received: 29 January 2014
Accepted: 2 May 2014

Abstract

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, ~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.

Conclusions.