The Magellanic Puzzle: origin of the periphery

In this paper, we analyse the metallicity structure of the Magellanic Clouds using parameters derived from the Gaia Data Release 3 (DR3) low-resolution XP (for Blue/Red Photometer) spectra, astrometry, and photometry. We find that the qualitative behaviour of the radial metallicity gradients in the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) is quite similar, with both of them having a metallicity plateau at intermediate radii and a second at larger radii. The LMC has a first metallicity plateau at [M/H] approximate to -0.8 for 3-7 degrees, while the SMC has one at [M/H] approximate to -1.1 for 3-5 degrees. The outer LMC periphery has a fairly constant metallicity of [M/H] approximate to -1.0 (10-18 degrees), while the outer SMC periphery has a value of [M/H] approximate to -1.3 (6-10 degrees). The sharp drop in metallicity in the LMC at similar to 8 degrees and the marked difference in age distributions in these two regions suggest that there were two important evolutionary phases in the LMC. In addition, we find that the Magellanic periphery substructures, likely Magellanic debris, are mostly dominated by LMC material stripped off in old interactions with the SMC. This presents a new picture in contrast with the popular belief that the debris around the clouds had been mostly stripped off from the SMC due to having a lower mass. We perform a detailed analysis for each known substructure and identify its potential origin based on metallicities and motions with respect to each galaxy.