Bar pattern speed modulation across Large Magellanic Cloud stellar populations

The bar pattern speed of the Large Magellanic Cloud (LMC) has been measured using Gaia data, suggesting the presence of a slow pattern that is perhaps not rotating at all. Numerical simulations of interacting LMC-SMC systems were able to reproduce a bar stoppage. Here, we report on the first measurement of the bar pattern speed of the LMC as a function of the evolutionary phase of its stellar populations. Astrometric and photometric data of ∼11 million LMC stars from Gaia DR3 were used to build five evolutionary phases, from less to more evolved stars. The Dehnen method, a new procedure to derive bar pattern speeds from kinematics of particles in N-body simulations, was applied to the LMC stellar populations. We observe a modulation of the bar pattern speed with the evolutionary phase, meaning that different LMC stellar populations exhibit different pattern speeds, ranging from −0.9 to 6.6 km s −1 kpc −1 . Moreover, less evolved stars have a lower pattern speed, while the bar of more evolved phases tends to rotate faster. The LMC bar is thus extremely slow, ruling out the presence of bar corotation within the disc, in agreement with a previous claim, but this time observed with various stellar populations. It is the first time that a pattern speed is measured separately for different stellar populations in any galaxy. The LMC pattern speed cannot be simply resumed to a singular value, but instead is an overlay of different patterns depending on the evolutionary phase of the stars. Future Gaia releases will be crucial to investigate more deeply the relations of the pattern speed with important astrophysical parameters of stars, such as their age and metallicity, which will be helpful to constrain the chemo-dynamical evolution of the LMC bar.