The age-metallicity relationship in the Fornax spheroidal dwarf galaxy

A.E. PIATTI; A. DEL PINO, A. APARICIO, S.L. HIDALGO

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2014 vol. 443 p. 1748 - 1753

0035-8711

We produce a comprehensive field star age-metallicity relationship (AMR) from the earliest epoch until $sim$ 1 Gyr ago for three fields in the Fornax dSph galaxy by using $VI$ photometric data obtained with $FORS1$ at the $VLT$. We find that the innermost one does not contains dominant very old stars (age $>$ 12 Gyr), whereas the relatively outer field does not account for representativestar field populations younger than $sim$ 3 Gyr. When focusing on the most prominent stellarpopulations, we find that the derived AMRs are engraved by the evidence of a outside-in star formation process. The studied fields show bimodal metallicity distributions peaked at [Fe/H] = (-0.95 $pm$ 0.15) dex and (-1.15 or -1.25 $pm$ 0.05) dex, respectively, but only during the first halfof the entire galaxy lifetime. Furthermore, the more metal-rich population appears to be more numerousin the outer fields, while in the innermost Fornax field the contribution of both metallicity populations seems to be similar.We also find that the metallicity spread $sim$ 6 Gyr ago is remarkable large, while the intrinsic metallicity dispersion at $sim$ 1-2 Gyr results smaller than that for the relatively older generations of stars. We interpret these outcomes as a result of a posssible merger of two galaxies that would have triggered a star formation bursting process that peaked between $sim$ 6 and 9 Gyr ago, depending on the position of the field in the galaxy.