HI mapping of the Leo Triplet: Morphologies and kinematics of tails and bridges

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.
A fully sampled and hitherto highest resolution and sensitivity observation of neutral hydrogen (H I) in the Leo Triplet (NGC 3628, M 65/NGC 3623, and M 66/NGC 3627) reveals six H I structures beyond the three galaxies. We present detailed results of the morphologies and kinematics of these structures, which can be used for future simulations. In particular, we detect a two-arm structure in the plume of NGC 3628 for the first time, which can be explained by a tidal interaction model. The optical counterpart of the plume is mainly associated with the southern arm. The connecting part (base) of the plume (directed eastward) with NGC 3628 is located at the blueshifted (western) side of NGC 3628. Two bases appear to be associated with the two arms of the plume. A clump with a reversed velocity gradient (relative to the velocity gradient of M 66) and a newly detected tail, that is to say M 66SE, is found in the southeast of M 66. We suspect that M 66SE represents gas from NGC 3628, which was captured by M 66 in the recent interaction between the two galaxies. Meanwhile gas is falling toward M 66, resulting in features previously observed in the southeastern part of M 66, such as large line widths and double peaks. An upside-down “Y”-shaped H I gas component (M 65S) is detected in the south of M 65, which suggests that M 65 may also have been involved in the interaction. We strongly encourage modern hydrodynamical simulations of this interacting group of galaxies to reveal the origin of the gaseous debris surrounding all three galaxies. © G. Wu et al. 2022.
This work was funded by the CAS “Light of West China” Program under grant No. 2018-XBQNXZ-B-024 and the National Natural Science foundation of China under grant Nos. 11433008, 12173075, 12103082, and 11973076. G.W. acknowledges the support from Youth Innovation Promotion Association CAS. DMD acknowledges financial support from the Talentia Senior Program (through the incentive ASE-136) from Secretaría General de Universidades, Investigación y Tecnología, de la Junta de Andalucía. DMD acknowledges funding from the State Agency for Research of the Spanish MCIU through the “Center of Excellence Severo Ochoa” award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709). DMD acknowledges funding from the State Agency for Research of the Spanish MCI (Project PID2020-114581GB-C21/AEI/10.13039/501100011033). This research made use of astrodendro, a Python package to compute dendrograms of Astronomical data (http://www.dendrograms.org/). The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The Arecibo Observatory is a facility of the National Science Foundation operated under cooperative agreement by the University of Central Florida and in alliance with Universidad Ana G. Mendez, and Yang Enterprises, Inc.