H I mapping of the Leo Triplet

Morphologies and kinematics of tails and bridges

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: gwu@mpifr-bonn.mpg.de
² Xinjiang Astronomical Observatory, Chinese Academy of Sciences, 830011 Urumqi, Xinjiang, PR China
³ Instituto de Astrofísica de Andalucía, CSIC, 18080 Granada, Spain
⁴ Astronomy Department, King Abdulaziz University, PO Box 80203 Jeddah 21589, Saudi Arabia
⁵ Helmholtz-Institut für Strahlen und Kernphysik (HISKP), University of Bonn, Nussallee 14-16, 53115 Bonn, Germany
⁶ Charles University in Prague, Faculty of Mathematics and Physics, Astronomical Institute, V Holešovičkách 2, 18000 Praha, Czech Republic
⁷ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁸ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
⁹ National Research Council Canada, Herzberg Programs in Astronomy and Astrophysics, Dominion Radio Astrophysical Observatory, PO Box 248 Penticton, BC V2A 6J9, Canada
¹⁰ Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101, USA
¹¹ Asociación Astronómica AstroHenares, 28823 Coslada, Madrid, Spain

Received: 16 June 2021
Accepted: 22 October 2021

Abstract

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.