CaTaclysm in the SMC - star clusters vs. field stars

D. GEISLER; M.C. PARISI; J.J. CLARIÁ; S. VILLANOVA; N. MARCIONNI; A. SARAJEDINI; A. GROCHOLSKI; G. CARRARO

Hawaii

Congreso; IAU General Assembly Meeting #29; 2015

We present new results based on VLT Ca Triplet (CaT) medium resolutionspectroscopy of some 200 red giantmembers of 29 SMC intermediate - oldage clusters. We derive mean cluster velocities to a few km/s and meanmetallicities to 0.05 dex. We also derive accurate velocities andmetallicities for about 750 surrounding field giants. We investigate themetallicity distribution, age-metallicity relation and metallicitygradient in great detail for the SMC using this large and homogeneousdatabase. We find a number of interesting results and some surprisingdifferences between the clusters and fields. The clusters display alikely bimodal metallicity distribution while the field stars areunimodal. The clusters show no strong evidence of a metallicity gradientwhile the field stars show a strong negative gradient in the innerregion of the galaxy that appears to reverse sign in the outer region.The difference between the cluster metallicity and the mean of thesurrounding field stars is a strong function of the cluster metallicity.The age-metallicity relation of the clusters shows a significantintrinsic metallicity dispersion at all ages, and no satisfactory fit toany current chemical evolution model. We discuss these results and theirimplications for the formation and evolution of the SMC.