SMASHing THE LMC: Mapping a Ring-like Stellar Overdensity in the LMC Disk

TL;DR

This study identifies a large, ring-like stellar overdensity in the LMC disk using survey data, suggesting it results from tidal interactions with the SMC, and provides insights into the galaxy's recent dynamical history.

Contribution

The paper reports the discovery of a continuous, ring-like stellar overdensity in the LMC disk and discusses its possible formation mechanisms related to interactions with the SMC.

Findings

Detected a ring-like overdensity at ~6 degrees radius in the LMC.

Overdensity correlates with intermediate-age star clusters.

Possible origins include tidal interactions or spiral arm formation.

Abstract

We explore the stellar structure of the Large Magellanic Cloud (LMC) disk using data from the Survey of the MAgellanic Stellar History (SMASH) and the Dark Energy Survey. We detect a ring-like stellar overdensity in the red clump star count map at a radius of ~6 degrees (~5.2 kpc at the LMC distance) that is continuous over ~270 degrees in position angle and is only limited by the current data coverage. The overdensity shows an amplitude up to 2.5 times higher than that of the underlying smooth disk. This structure might be related to the multiple arms found by de Vaucouleurs. We find that the overdensity shows spatial correlation with intermediate-age star clusters, but not with young (< 1 Gyr) main-sequence stars, indicating the stellar populations associated with the overdensity are intermediate in age or older. Our findings on the LMC overdensity can be explained by either of two distinct formation mechanisms of a ring-like overdensity: (1) the overdensity formed out of an asymmetric one-armed spiral wrapping around the LMC main body, which is induced by repeated encounters with the Small Magellanic Cloud (SMC) over the last Gyr, or (2) the overdensity formed very recently as a tidal response to a direct collision with the SMC. Although the measured properties of the overdensity alone cannot distinguish between the two candidate scenarios, the consistency with both scenarios suggests that the ring-like overdensity is likely a product of tidal interaction with the SMC, but not with the Milky Way halo.