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A History of H i Stripping in Virgo: A Phase-space View of VIVA Galaxies
Yoon, Hyein,Chung, Aeree,Smith, Rory,Jaffé,, Yara L. American Astronomical Society 2017 The Astrophysical Journal Vol.838 No.2
<P>We investigate the orbital histories of Virgo galaxies at various stages of HI gas stripping. In particular, we compare the location of galaxies with different HI morphology in phase space. This method is a great tool for tracing the gas stripping histories of galaxies as they fall into the cluster. Most galaxies at the early stage of HI stripping are found in the first infall region of Virgo, while galaxies undergoing active HI stripping mostly appear to be falling in or moving out near the cluster core for the first time. Galaxies with severely stripped, yet symmetric, HI disks are found in one of two locations. Some are deep inside the cluster, but others are found in the cluster outskirts with low orbital velocities. We suggest that the latter group of galaxies belong to a 'backsplash' population. These present the clearest candidates for backsplashed galaxies observationally identified to date. We further investigate the distribution of a large sample of HI-detected galaxies toward Virgo in phase space, confirming that most galaxies are stripped of their gas as they settle into the gravitational potential of the cluster. In addition, we discuss the impact of tidal interactions between galaxies and group preprocessing on the HI properties of the cluster galaxies, and link the associated star formation evolution to the stripping sequence of cluster galaxies.</P>
RECENT GALAXY MERGERS AND RESIDUAL STAR FORMATION OF RED SEQUENCE GALAXIES IN GALAXY CLUSTERS
Sheen, Yun-Kyeong,Yi, Sukyoung K.,Ree, Chang H.,Jaffé,, Yara,Demarco, Ricardo,Treister, Ezequiel American Astronomical Society 2016 The Astrophysical journal Vol.827 No.1
<P>This study explored the Galaxy Evolution Explorer ultraviolet (UV) properties of optical red sequence galaxies in four rich Abell clusters at z <= 0.1. In particular, we tried to find a hint of merger-induced recent star formation (RSF) in red sequence galaxies. Using the NUV - r' colors of the galaxies, RSF fractions were derived based on various criteria for post-merger galaxies and normal galaxies. Following k-correction, about 36% of the post-merger galaxies were classified as RSF galaxies with a conservative criterion (NUV - r' <= 5), and that number was doubled (similar to 72%) when using a generous criterion (NUV - r' <= 5.4). The trend was the same when we restricted the sample to galaxies within 0.5 x R-200. Post-merger galaxies with strong UV emission showed more violent, asymmetric features in the deep optical images. The RSF fractions did not show any trend along the clustocentric distance within R-200. We performed a Dressler-Shectman test to check whether the RSF galaxies had any correlation with the substructures in the galaxy clusters. Within R-200 of each cluster, the RSF galaxies did not appear to be preferentially related to the clusters' substructures. Our results suggested that only 30% of RSF red sequence galaxies show morphological hints of recent galaxy mergers. This implies that internal processes (e.g., stellar mass loss or hot gas cooling) for the supply of cold gas to early-type galaxies may play a significant role in the residual star formation of early-type galaxies at a recent epoch.</P>