Letter to the Editor

The Large Magellanic Cloud stellar content with SMASH

I. Assessing the stability of the Magellanic spiral arms

¹ Instituto de Astrofísica de Canarias, Calle Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
e-mail: tomasruizlara@gmail.com
² Departamento de Astrofísica, Universidad de La Laguna, 38200 La Laguna, Tenerife, Spain
³ Department of Physics, Montana State University, PO Box 173840, Bozeman, MT 59717-3840, USA
⁴ NSF’s National Optical-Infrared Astronomy Research Laboratory, 950 North Cherry Ave, Tucson, AZ 85719, USA
⁵ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁶ Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
⁷ Université Côte d’Azur, OCA, CNRS, Lagrange, France
⁸ INAF – Astronomical Observatory of Abruzzo, Via M. Maggini, s/n, 64100 Teramo, Italy
⁹ INFN, Sezione di Pisa, Largo Pontecorvo 3, 56127 Pisa, Italy
¹⁰ Department of Physics, University of Surrey, Guildford GU2 7XH, UK
¹¹ Departamento de Física Teórica y del Cosmos, Universidad de Granada, Campus de Fuentenueva, 18071 Granada, Spain
¹² Instituto Carlos I de Física Teórica y computacional, Universidad de Granada, 18071 Granada, Spain
¹³ Department of Physics and Astronomy, University College London, Gower Street, WC1E 6BT London, UK
¹⁴ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
¹⁵ Department of Astronomy, University of Virginia, Charlottesville, VA 22904-4325, USA
¹⁶ Center for Astrophysical Sciences, Department of Physics & Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA
¹⁷ Instituto de Astrofísica de Andalucía, CSIC, 18080 Granada, Spain
¹⁸ Instituto de Investigación Multidisciplinar en Ciencia y Tecnología, Universidad de La Serena, Raúl Bitrán 1305, La Serena, Chile
¹⁹ Departamento de Astronomía, Universidad de La Serena, Av. Juan Cisternas 1200 Norte, La Serena, Chile
²⁰ Isaac Newton Group of Telescopes, Apartado 321, 38700 Santa Cruz de La Palma, Canary Islands, Spain
²¹ Departamento de Astronomía, Universidad de Chile, Camino del Observatorio 1515, Las Condes, Santiago, Chile
²² Center for Astrophysics and Space Astronomy, University of Colorado, 389 UCB, Boulder, CO 80309-0389, USA
²³ Cerro Tololo Inter-American Observatory, NSF’s National Optical-Infrared Astronomy Research Laboratory, Casilla 603, La Serena, Chile

Received: 11 May 2020
Accepted: 8 June 2020

Abstract

The Large Magellanic Cloud (LMC) is the closest and most studied example of an irregular galaxy. Among its principal defining morphological features, its off-centred bar and single spiral arm stand out, defining a whole family of galaxies known as the Magellanic spirals (Sm). These structures are thought to be triggered by tidal interactions and possibly maintained via gas accretion. However, it is still unknown whether they are long-lived stable structures. In this work, by combining photometry that reaches down to the oldest main sequence turn-off in the colour-magnitude diagrams (CMD, up to a distance of ∼4.4 kpc from the LMC centre) from the SMASH survey and CMD fitting techniques, we find compelling evidence supporting the long-term stability of the LMC spiral arm, dating the origin of this structure to more than 2 Gyr ago. The evidence suggests that the close encounter between the LMC and the Small Magellanic Cloud (SMC) that produced the gaseous Magellanic Stream and its Leading Arm also triggered the formation of the LMC’s spiral arm. Given the mass difference between the Clouds and the notable consequences of this interaction, we can speculate that this should have been one of their closest encounters. These results set important constraints on the timing of LMC-SMC collisions, as well as on the physics behind star formation induced by tidal encounters.