This is an Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Cluster substructure and ram pressure stripping in individual galaxies are among the primary pieces of evidence for the ongoing growth of galaxy clusters as they accrete galaxies and groups from their surroundings. We present a multiwavelength study of the center of the Hydra I galaxy cluster, including exquisite new MeerKAT H I and DECam Hα imaging which reveal conclusive evidence for ram pressure stripping in NGC 3312, NGC 3314a, and NGC 3314b through compressed H I contours, well-defined H I tails, and ongoing star formation in the stripped gas. In particular, we quantify the stripped material in NGC 3312, and NGC 3314a, which makes up between 8% and 35% of the gas still in the disk, is forming stars at ∼0.5 M⊙ yr−1, and extends ∼30−60 kpc from the main disk. The estimated stellar mass in the tails is an order of magnitude less than the H I mass. A fourth “ring” galaxy at the same velocity does not show signs of ram pressure in H I. In addition, we used the H I and stellar morphologies, combined with a Beta model of the hot intracluster medium, to constrain the real distances of the galaxies to the cluster center, and we used the chance alignment of NGC 3314b behind NGC 3314a to break the degeneracy between whether the galaxies are in front or in back of the cluster. The drag seen in the H I tails supports our preferred scenario that NGC 3312 and NGC 3314a are moving toward us as part of a foreground substructure which has already passed its pericenter and is on “out fall” from the cluster. The high surviving H I content of the galaxies may suggest that the substructure or intragroup medium can protect them from the harshest effects of ram pressure, or that the galaxies are in fact on more tangential orbits. © The Authors 2022.
K.M.H. acknowledges financial support from the State Agency for Research of the Spanish Ministry of Science, Innovation and Universities through the “Center of Excellence Severo Ochoa” awarded to the Instituto de Astrofísica de Andalucía (SEV-2017-0709) from the coordination of the participation in SKA-SPAIN, funded by the Ministry of Science and innovation (MICIN) and grant RTI2018-096228-B-C31 (MCIU/AEI/FEDER,UE). R.K. gratefully acknowledges partial funding support from the National Aeronautics and Space Administration under project 80NSSC18K1498, and from the National Science Foundation under grants No. 1852136 and 2150222. H.C. is supported by Key Research Project of Zhejiang Lab. (No. 2021PE0AC03); the South African Department of Science and Innovation and the National Research Foundation through SARChI’s South African SKA Fellowship within the SARAO Research Chair held by RC Kraan-Korteweg. J.S.G. thanks the University of Wisconsin College of Letters and Science for partial support of this work. The MeerKAT telescope is operated by the South African Radio Astronomy Observatory, which is a facility of the National Research Foundation, an agency of the Department of Science and Innovation. Part of the data published here have been reduced using the CARACal pipeline, partially supported by ERC Starting grant number 679629 “FORNAX”, MAECI Grant Number ZA18GR02, DST-NRF Grant Number 113121 as part of the ISARP Joint Research Scheme, and BMBF project 05A17PC2 for D-MeerKAT, and partially supported by the South African Research Chairs Initiative of the Department of Science and Technology and National Research Foundation. Information about CARACal can be obtained online under the URL: https://caracal.readthedocs.io/en/latest. This work made use of the CARTA (Cube Analysis and Rendering Tool for Astronomy) software (DOI: https://doi.org/10.5281/zenodo.3377984 – https://cartavis.github.io). We acknowledge the use of the Ilifu cloud computing facility – www.ilifu.ac.za, a partnership between the University of Cape Town, the University of the Western Cape, the University of Stellenbosch, Sol Plaatje University, the Cape Peninsula University of Technology and the South African Radio Astronomy Observatory. The Ilifu facility is supported by contributions from the Inter-University Institute for Data Intensive Astronomy (IDIA – a partnership between the University of Cape Town, the University of Pretoria, the University of the Western Cape and the South African Radio astronomy Observatory), the Computational Biology division at UCT and the Data Intensive Research Initiative of South Africa (DIRISA).