Letter to the Editor

Evidence of ram-pressure stripping of WLM, a dwarf galaxy far away from any large host galaxy

¹ GEPI, Observatoire de Paris, Universite PSL, CNRS, Place Jules Janssen, 92195 Meudon, France
e-mail: yanbin.yang@obspm.fr
² Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía, 18008 Granada, Spain
³ Department of Physics and Electronics, Rhodes University, PO Box 94, Makhanda 6140, South Africa
⁴ South African Radio Astronomy Observatory, 2 Fir Street, Black River Park, Observatory, Cape Town 7925, South Africa
⁵ Physics & Astronomy Department, University of Victoria, 3800 Finnerty Rd, Victoria, B.C. V8P 5C2, Canada
⁶ Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa
⁷ Département de physique, Université de Montréal, Complexe des sciences MIL, 1375 Avenue Thérèse-Lavoie-Roux, Montréal, Qc H2V 0B3, Canada
⁸ Laboratoire de Physique et de Chimie de l’Environnement, Observatoire d’Astrophysique de l’Université Ouaga I Pr Joseph Ki-Zerbo (ODAUO), BP 7021 Ouaga 03, Burkina Faso
⁹ Max-Planck-Institut für Radioastronomie, Radioobservatorium Effelsberg, Max-Planck-Straße 28, 53902 Bad Münstereifel, Germany
¹⁰ NRC Herzberg Astronomy and Astrophysics, 5071 West Saanich Road, Victoria, B.C. V9E 2E7, Canada

Received: 10 February 2022
Accepted: 28 March 2022

Abstract

Dwarf galaxies are affected by all the evolutionary processes normally at work in galaxies of any mass. As fainter and less massive galaxies, however, dwarf galaxies are particularly susceptible to environmental mechanisms that can more easily perturb these systems. Importantly, the presence of nearby large galaxies is expected to have a profound effect on dwarf galaxies. Gravitational (especially tidally induced) effects from the large galaxy can cause mass to be lost from the dwarf, and the passage of the dwarf through the gaseous medium surrounding the large galaxy can additionally cause the dwarf to lose its own gas through a process called ram-pressure stripping. Such effects are considered to be the main sources of difference between “satellite” and “field” dwarf galaxy populations. Here, we report on new observations of the gaseous content of Wolf–Lundmark–Melotte (WLM), an archetype of isolated, gas-rich field dwarf galaxies in the Local Universe, which presents a much more complex situation. Previous studies of its gaseous disk suggest it has perturbed kinematics; here, we identify four trailing, extended gas clouds lying in the direction opposite to WLM’s spatial motion, as well as a spatial offset between the WLM gas and stars. Overall, the morphology and kinematics of this gas show that WLM is undergoing ram-pressure stripping, despite being 930 and 830 kpc from the Milky Way and M 31, respectively. This finding indicates the presence of an intergalactic, gaseous reservoir far from large galaxies whose evolutionary role in galaxies, both large and small, may not be fully appreciated.