POST-MERGER SIGNATURES OF RED-SEQUENCE GALAXIES IN RICH ABELL CLUSTERS AT z ≲ 0.1

Abstract

We have investigated the post-merger signatures of red-sequence galaxies in rich Abell clusters at z 0.1: A119, A2670, A3330 and A389. Deep images in u , g , r and medium-resolution galaxy spectra were taken using MOSAIC 2 CCD and Hydra MOS mounted on a Blanco 4-m telescope at CTIO. Post-merger features are identified by visual inspection based on asymmetric disturbed features, faint structures, discontinuous halo structures, rings and dust lanes. We found that ∼ 25% of bright (M r < −20) cluster red-sequence galaxies show post-merger signatures in four clusters consistently. Most (∼ 71%) of the featured galaxies were found to be bulge-dominated, and for the subsample of bulge-dominated red-sequence galaxies, the post-merger fraction rises to ∼ 38%. We also found that roughly 4% of bulge-dominated red-sequence galaxies interact (on-going merger). A total of 42% (38% post-merger, 4% on-going merger) of galaxies show merger-related features. Compared to a field galaxy study with a similar limiting magnitude (van Dokkum 2005), our cluster study presents a similar post-merger fraction but a markedly lower on-going merger fraction. The merger fraction derived is surprisingly high for the high density of our clusters, where the fast internal motions of galaxies are thought to play a negative role in galaxy mergers. The fraction of post-merger and ongoing merger galaxies can be explained as follows. Most of the post-merger galaxies may have carried over their merger features from their previous halo environment, whereas interacting galaxies interact in the current cluster in situ. According to our semi-analytic calculation, massive cluster haloes may very well have experienced tens of halo mergers over the last 4-5 Gyr; post-merger features last that long, allowing these features to be detected in our clusters today. The apparent lack of dependence of the merger fraction on the clustocentric distance is naturally explained this way. In this scenario, the galaxy morphology and properties can be properly interpreted only when the halo evolution characteristics are understood first.

Merger relics of cluster galaxies

“…The dust-to-gas ratios associated with metal abundances in their studies are close to those of Milky Way (Alton et al 1998;Davies et al 1999). Then, we synthesized mock images by using the same filters as in the observations of Sheen et al (2012). Merger features in these synthetic images are spectacular and long-lasting.…”

The Preferential Tidal Stripping of Dark Matter Versus Stars in Galaxies

“…The presence of kinematically decoupled cores in some cluster dwarf ellipticals could be direct evidence for the influence of the group environment (Toloba et al (2014)), as it is very difficult to form such features by harassment (González-García et al 2005). The high frequency of cluster galaxies with merger features may also provide evidence for preprocessing (Sheen et al 2012;Yi et al 2013).…”

The Sami Galaxy Survey: Galaxy Interactions and Kinematic Anomalies in Abell 119

“…Since mergers cause distortions in the morphology of the system, visual inspections of images are often used to trace recent mergers. Deep images are therefore essential for detecting evidence of mergers and interactions, and reveal that galaxies have assembled a substantial fraction of their mass via mergers even in recent epochs (van Dokkum 2005;Tal et al 2009;Kaviraj 2010b;Sheen et al 2012;Yi et al 2013;Duc et al 2015).…”