The Chemical Enrichment History of the Fornax Dwarf Spheroidal Galaxy from the Infrared Calcium Triplet

• DOI: 10.1086/380608
• Publication Date: 2004-02-23T16:43:00Z
• Authors: Frdric Pont; Robert Zinn; Carme Gallart; Eduardo Hardy; Rebeccah Winnick
• Keywords: Red-giant branch; Dwarf spheroidal galaxy; Stellar population

Near-infrared spectra were obtained for 117 red giants in the Fornax dwarf spheroidal galaxy with FORS1 spectrograph on VLT, order to study metallicity distribution of stars and lift age-metallicity degeneracy giant branch (RGB) color-magnitude diagram (CMD). Metallicities are derived from equivalent widths infrared calcium triplet lines at 8498, 8542, 8662 Å, calibrated data globular clusters, open cluster M67, LMC. For a substantial portion sample, strength is unexpectedly high, clearly indicating that main stellar population significantly more metal-rich than could be inferred position its RGB CMD. We show relative narrowness caused by superposition very different ages metallicities. The region parameter space occupied most Fornax—young, metal-rich, luminous—is not covered any calibrating which introduces uncertainty high end scale. Using published theoretical calculations Ca II widths, we have investigated their sensitivity luminosity, age, metallicity. correlation between absolute I magnitude appears only slightly affected age variations, used it estimate metallicities stars. centered [Fe/H] = -0.9, metal-poor tail extending ≃ -2. While higher less well determined our observations, comparison LMC indicates extends ∼ -0.4. By comparing positions CMD, complex relation Fornax. In first few gigayears, metal abundance rose -1.0 dex. enrichment accelerated past ∼1–4 Gyr reach -0.4 More half sample constituted younger ∼4 Gyr, thus sustained recent star formation These results briefly compared predictions evolution galaxies. They indicate capacity galaxies retain heavy elements they produce larger expected.