Seminaire Lagrange -- Laurent Chemin (Strasburg) -- The pattern speed of the stellar bar of the Large Magellanic Cloud measured with Gaia data

The pattern speed of the stellar bar of the Large Magellanic Cloud measured with Gaia data

The Large Magellanic Cloud, the mini barred spiral galaxy distant by 50 kpc from the Milky Way, has been observed extensively bycthe ESA-Gaia satellite since 2014. For about 11 million stars, the LMC disc velocity components have been inferred using Gaia astrometry, from which stellar orbits can be studied, and particularly in the region of the LMC bar. I will present results of measuring the most fundamental parameter of the LMC bar, its pattern speed, by means of three different methods. It is shown that the most popular method, which estimated bar pattern speeds for hundreds of galaxies, fails to give a coherent result for the LMC. A more appropriate method involving elliptical orbits and asymmetric rotational motions finds a LMC bar pattern speed of ~18.5 km/s/kpc, corresponding to a rotation period of 330 Myrs. This would make the LMC hosting a slow bar, which is at odds with most of the fast bars found in the Local Universe.