The VMC Survey - XIV. First results on the look-back time star-formation rate tomography of the Small Magellanic Cloud

S. RUBELE, L. GIRARDI, L. KERBER, M.-R.L. CIONI; A.E. PIATTI; +14 CO-AUTHORS

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2015 vol. 449 p. 639 - 661

0035-8711

We analyse deep images collected by the VISTA survey of the Magellanic Cloudsin the Y JKs filters, covering a total area of 14 deg2 (10 tiles) and comprising themain body and Wing of the Small Magellanic Cloud (SMC). This area is split into120 subregions, which are analysed via a colour?magnitude diagram reconstructionmethod that returns their best-fitting star formation rate SFR(t), age?metallicityrelation (AMR), distance and mean reddening, together with 68% confidence intervals.The distance data can be fit by a plane tilted in the east-west direction with a meaninclination of 39◦ ; deviations however amount to up to ±3 kpc and point to a distortedand warped disk. The only region found with a significant spread along the line-of-sightis the south-east end of the Wing. After assigning to every observed star a probabilityof belonging to a given age?metallicity interval, we build high-resolution maps of theSMC populations. They dramatically reveal the flocculant nature of the young starformation, and the nearly smooth features drawn by the older stellar generations. Theydocument the formation of the SMC Wing at ages < 0.2 Gyr, and the peak of starformation in the SMC Bar at ∼ 40 Myr. We clearly detect periods of enhanced starformation at ages of 1.5 and 5 Gyr. The former is possibly related to a new featurewe find in the AMR, which points to the ingestion of metal-poor gas at ages slightlylarger than 1 Gyr. The latter constitutes a major period of stellar mass formation inthe SMC. We confirm that the SFR(t) was moderately low at even older ages.