The Magellanic Puzzle: origin of the periphery

Abstract

In this paper, we analyse the metallicity structure of the Magellanic Clouds using parameters derived from the Gaia DR3 low-resolution XP spectra, astrometry and photometry. We find that the qualitative behavior of the radial metallicity gradients in the LMC and SMC are 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 [Fe/H]$\approx$-0.8 for 3$-$7$^{\circ}$, while the SMC has one at [Fe/H]$\approx$-1.1 at 3$-$5$^{\circ}$. The outer LMC periphery has a fairly constant metallicity of [Fe/H]$\approx$-1.0 (10$-$18$^{\circ}$), while the outer SMC periphery has a value of [Fe/H]$\approx$-1.3 (6$-$10$^{\circ}$). The sharp drop in metallicity in the LMC at $\sim$8$^{\circ}$ and the marked difference in age distributions in these two regions suggests 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.