Astronomy

Merger Relics

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Science  19 Jul 2013:
Vol. 341, Issue 6143, pp. 216
DOI: 10.1126/science.341.6143.216-a
CREDIT: NASA, HOLLAND FORD (JHU), THE ACS SCIENCE TEAM AND ESA

Massive galaxies are thought to form through a succession of mergers between smaller galaxies. These interactions are expected to be more frequent in regions where there are fewer galaxies; in high-density regions, galaxies move faster and mergers are less likely. However, a recent study has revealed that 38% of massive galaxies in heavy clusters of galaxies show features that are consistent with the merging of galaxies (such as tidal tails). To try to explain this unexpected result, Yi et al. ran a cosmological-volume simulation to derive the merger history of dark-matter halos, then constructed semi-analytical models of galaxies to populate those halos, and finally performed hydrodynamical simulations of galaxy-galaxy mergers to estimate the lifetime of merger features. Merger features are expected to last very long in clusters of galaxies. Thus, when observed there, they may not be the result of recent in situ mergers but relics from interactions that happened when the galaxies were in a different environment.

Astron. Astrophys. 554, A122 (2013).

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