Spatially resolved LMC star formation history - I. outside in evolution of the outer LMC disc

Abstract

We study the evolution of three fields in the outer Large Magellanic Cloud (LMC) disc (Rgc = 3.5-6.2 kpc). Their star formation history indicates a stellar population gradient such that younger stellar populations are more centrally concentrated. We identify two main starforming epochs, separated by a period of lower activity between ≃7 and ≃4Gyr ago. Their relative importance varies from a similar amount of stars formed in the two epochs in the innermost field to only 40 per cent of the stars formed in the more recent epoch in the outermost field. The young star-forming epoch continues to the present time in the innermost field, but lasted only till ≃ 0.8 and 1.3Gyr ago at Rgc = 5°.5 and 7°.1, respectively. This gradient is correlated with the measured HI column density and implies an outside-in quenching of the star formation, possibly related to a variation of the size of the HI disc. This could either result from gas depletion due to star formation or ram-pressure stripping, or from to the compression of the gas disc as ram pressure from the MilkyWay halo acted on the LMCinterstellarmedium. The latter two situations may have occurred when the LMC first approached the Milky Way. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.