The age-metallicity relationship in the Small Magellanic Cloud periphery

Abstract

We present results from Washington CT1 photometry for 11 star fields located in the western outskirts of the Small Magellanic Cloud (SMC), which cover angular distances to its centre from 2° up to 13° (≈2.2-13.8 kpc). The colour-magnitude diagrams, cleaned from the unavoidable Milky Way (MW) and background galaxy signatures, reveal that the most distant dominant main-sequence (MS) stellar populations from the SMC centre are located at an angular distance of ~5°.7 (6.1 kpc); no sign of farther clear SMC MS is visible other than the residuals from the MW/background field contamination. The derived ages and metallicities for the dominant stellar populations of the western SMC periphery show a constant metallicity level ([Fe/H] = -1.0 dex) and an approximately constant age value (≈7-8 Gyr). Their age-metallicity relationship (AMR) do not clearly differ from the most comprehensive AMRs derived for almost the entire SMC main body. Finally, the range of ages of the dominant stellar populations in the western SMC periphery confirms that the major stellar mass formation activity at the very early galaxy epoch peaked ~7-8 Gyr ago.