LMC Cluster Abundances and Kinematics

We present results from a project aimed at better understanding the kinematics and metallicities of populous clusters in the LMC. We have utilized FORS2 on the VLT to obtain infrared spectra for more than 200 stars in 28 LMC clusters spanning a large range of ages (~ 1–13 Gyr) and metallicities (-0.3 > [Fe/H] > -2.0). The absorption lines of the calcium II triplet were then used to calculate radial velocities and [Fe/H]. We determine mean cluster velocities to typically 1.6 km s-1 and mean metallicities to 0.04 dex (random error). Similar to what was found by previous authors, this cluster sample has motions consistent with that of a single rotating disk system, with no indication of halo kinematics. However, in contrast to previous work, we find that the higher metallicity clusters in our sample show a very tight [Fe/H] distribution with no tail toward solar metallicities. The cluster distribution is similar to what has been found for red giant stars in the bar, which indicates that the bar and the intermediate age clusters have similar star formation histories. This is in good agreement with recent theoretical models that suggest the bar and intermediate age clusters formed as a result of a close encounter with the SMC. Our findings also confirm previous results which show that the LMC lacks the metallicity gradient typically seen in non-barred spiral galaxies, suggesting that the bar is driving the mixing of stellar populations in the LMC.