The star field age-metallicity relationship of the Small Magellanic Cloud

PIATTI, ANDRÉS E.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2012 vol. 422 p. 1109 - 1121

0035-8711

We present the results of the age and metallicity estimates for the unprecedented database of some 3.3 millionof stars distributed throughout the entire Small MagellanicCloud (SMC) main body, obtained for the first time from CCD Washington $CT_1$ photometry. We produce the first comprehensive  star field AMR from the birth of the galaxy until $sim$ 1 Gyr ago, independent of any other previous approach. We find that the field stars do not possess gradients in age and metallicity, and that stellar populations formed since $sim$ 2 Gyr ago are more metal-rich than [Fe/H] $sim$ -0.8 dex and are confined to the innermost region (semi-major axis $la$ 1$degr$).  For the first time we compare, homogeneously, the present star field  AMR to that of the star cluster population with ages and metallicities in the same star field scales, and find that  clusters and star fields share similar chemical evolution histories. Both galaxy components have experienced two enhanced formation processes: the most recent peaked at an age of $sim$ 2 Gyr, and an earlier one detected at an age of $sim$ 5-6 and 7.5 Gyr for clusters and  star fields, respectively.