CHEMICAL EVOLUTION OF THE LARGE MAGELLANIC CLOUD

We adopt a new chemical evolution model for the Large Magellanic Cloud (LMC) and thereby investigate its past star formation and chemical enrichment histories. The delay time distribution of Type Ia supernovae recently revealed by Type Ia supernova surveys is incorporated self-consistently into the new model. The principle results are summarized as follows. The present gas mass fraction and stellar metallicity as well as the higher [Ba/Fe] in metal-poor stars at [Fe/H] < –1.5 can be more self-consistently explained by models with steeper initial mass functions. The observed higher [Mg/Fe] (≥0.3) at [Fe/H] ∼ –0.6 and higher [Ba/Fe] (>0.5) at [Fe/H] ∼ –0.3 could be due to significantly enhanced star formation about 2 Gyr ago. The observed overall [Ca/Fe]-[Fe/H] relation and remarkably low [Ca/Fe] (< – 0.2) at [Fe/H] > –0.6 are consistent with models with short-delay supernova Ia and with the more efficient loss of Ca possibly caused by an explosion mechanism of Type II supernovae. Although the metallicity distribution functions do not show double peaks in the models with a starburst about 2 Gyr ago, they show characteristic double peaks in the models with double starbursts ∼200 Myr and ∼2 Gyr ago. The observed apparent dip of [Fe/H] around ∼1.5 Gyr ago in the age-metallicity relation can be reproduced by models in which a large amount (∼109 M☉) of metal-poor ([Fe/H] < –1) gas can be accreted onto the LMC.