The bar pattern speed of the Large Magellanic Cloud

arXiv (Cornell University)

Abstract

Context: The Large Magellanic Cloud (LMC) internal kinematics have been studied in unprecedented depth thanks to the excellent quality of the Gaia mission data, revealing the disc's non-axisymmetric structure. Aims: We want to constrain the LMC bar pattern speed using the astrometric and spectroscopic data from the Gaia mission. Methods: We apply three methods to evaluate the bar pattern speed: it is measured through the Tremaine-Weinberg (TW) method, the Dehnen method and a bisymmetric velocity (BV) model. The methods provide additional information on the bar properties such as the corotation radius and the bar length and strength. The validity of the methods is tested with numerical simulations. Results: A wide range of pattern speeds are inferred by the TW method, owing to a strong dependency on the orientation of the galaxy frame and the viewing angle of the bar perturbation. The simulated bar pattern speeds (corotation radii, respectively) are well recovered by the Dehnen method (BV model). Applied to the LMC data, the Dehnen method finds a pattern speed Omega_p = -1.0 +/- 0.5 km s-1 kpc-1, thus corresponding to a bar which barely rotates, slightly counter-rotating with respect to the LMC disc. The BV method finds a LMC bar corotation radius of Rc = 4.20 +/- 0.25 kpc, corresponding to a pattern speed Omega_p = 18.5^{+1.2}_{-1.1} km s-1 kpc-1. Conclusions: It is not possible to decide which global value best represents an LMC bar pattern speed with the TW method, due to the strong variation with the orientation of the reference frame. The non-rotating bar from the Dehnen method would be at odds with the structure and kinematics of the LMC disc. The BV method result is consistent with previous estimates and gives a bar corotation-to-length ratio of 1.8 +/- 0.1, which makes the LMC hosting a slow bar.

Authors 9

1. Ó. Jiménez-Arranz
2. L. Chemin

   Universidad Andrés Bello

   Affiliation as printed

   Instituto de Astrofísica , Universidad Andres Bello , Fernandez Concha 700 , Las Condes , Santiago RM , Chile

3. Mercè Romero-Gómez
4. X. Luri
5. P. Adamczyk

   Universidad de Antofagasta

   Affiliation as printed

   Centro de Astronomía -CITEVA , Universidad de Antofagasta , Avenida Angamos 601 , Antofagasta 1270300 , Chile

6. A. Castro-Ginard Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory , Leiden University , Niels Bohrweg 2 , 2333 CA Leiden , The Netherlands

7. S. Roca-Fàbrega
8. P. J. McMillan

   Lund University

   Affiliation as printed

   Lund Observatory , Division of Astrophysics , Department of Physics , Lund University , Box 43 , SE-221 00 Lund , Sweden

9. Maria-Rosa L. Cioni

   Leibniz Institute for Astrophysics Potsdam

   Affiliation as printed

   Leibniz-Institut für Astrophysik Potsdam , An der Sternwarte 16 , D-14482 Potsdam , Germany