The Large Magellanic Cloud stellar content with SMASH: I. Assessing the stability of the Magellanic spiral arms
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. © ESO 2020. ; TRL, CG, MM, FS and LM acknowledge financial support through grants (AEI/FEDER, UE) AYA201789076-P, AYA2016-77237-C3-1-P (RAVET project) and AYA2015-63810-P, as well as by Ministerio de Ciencia, Innovacion y Universidades (MCIU), through Juan de la Cierva - Formacion grant (FJCI-2016-30342) and the State Budget and by Consejeria de Economia, Industria, Comercio y Conocimiento of the Canary Islands Autonomous Community, through Regional Budget. TRL also acknowledges support from the Spanish Public State Employment Service (SEPE). Y.C. acknowledges support from NSF grant AST 1655677. SC acknowledges support from Premiale INAF "MITIC" and grant AYA201342781P from the Ministry of Economy and Competitiveness of Spain, he has also been supported by INFN (Iniziativa specifica TAsP). M-RC acknowledges support from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement No. 682115). SRM acknowledges support through NSF grant AST-1909497. DMD acknowledges support through grant AYA2016-81065-C2-2 and through the "Centre of Excellence Severo Ochoa" award for the Instituto de Astrofisica de Andalucia (SEV-2017-0709) and from grant PGC2018-095049-B-C21. AM acknowledges financial support from FONDECYT Regular 1181797 and funding from the Max Planck Society through a Partner Group grant. R.R.M. acknowledges partial support from project BASAL AFB-170002 as well as FONDECYT project Nffi1170364. This research makes use of python (http://www.python.org); Matplotlib (Hunter 2007) and Astropy (Astropy Collaboration 2013, 2018). Based on observations at Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory (NOAO Prop. ID: 2013A-0411 and 2013B0440; PI: Nidever), which is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. This project used data obtained with the Dark Energy Camera (DECam), which was constructed by the Dark Energy Survey (DES) collaboration. Funding providers for the DES Projects can be found in https://www.darkenergysurvey.org/collaboration-and-sponsors/ ; Peer reviewed
