Jellyfish: A spectroscopic study of ram-pressure stripping in massive galaxy clusters[1] [1] Most of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The observatory was made possible by the generous finical support of the W.M. Keck Foundation.

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^†^†pubyear: 2016 Jellyfish: A spectroscopic study of ram-pressure stripping in massive galaxy clusters^†^†thanks: Most of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The observatory was made possible by the generous finical support of the W.M. Keck Foundation.

Harald Ebeling

Abstract

^†^†pubyear: 2016

We continue our exploration of ram-pressure stripping (RPS) in massive galaxy clusters at \(z{>}0.3\) by assessing the spectroscopic properties of RPS candidates selected previously on the grounds of their morphological appearance in Hubble Space Telescope images. We confirm cluster membership for 55 of our candidates, thereby tripling the number of RPS candidates known at \(z{>}0.2\). Although many of these systems are too faint and too distant for the kind of in-depth investigation required to unambiguously confirm or refute the presence of RPS, the ensemble properties of our sample are consistent with increased star formation, and many of the selected galaxies exhibit visible debris trails. Specifically, about two thirds of all galaxies exhibit line emission ([OII]\(\lambda\)3727Å, H\(\beta\), and, where observationally accessible, H\(\alpha\)) consistent with robust star-formation rates that significantly exceed those expected for systems on the galaxy main sequence. We find no significant dependence of either the presence of line emission or the inferred star-formation rate on the relaxation state of the host cluster.

Although we caution that our sample may contain not only galaxies undergoing RPS by the diffuse intra-cluster medium (ICM), but also minor mergers located at the low-density cluster outskirts and merely projected onto the cluster cores, we expect our results to facilitate and inform realistic process models of the stripping process by providing the first statistically significant sample of RPS candidates in truly massive clusters. While extremely rapid removal of the intrastellar medium is not ruled out by our findings, extended periods of triggered star formation are clearly an integral component of the physics of ICM-galaxy interaction in massive clusters.

Detailed studies of two of our candidates using integral-field spectroscopy are underway and will further test our RPS hypothesis by measuring the spatial distribution of star-formation activity and its correlation with intra-galactic bulk motions.