SMASHing the LMC: A Tidally-induced Warp in the Outer LMC and a Large-scale Reddening Map

TL;DR

This study maps the 3D structure of the Large Magellanic Cloud using red clump stars, revealing a significant warp in its outer disk likely caused by tidal interactions with the Small Magellanic Cloud, and providing a detailed reddening map.

Contribution

First detailed 3D mapping of the LMC's warp and reddening using RC stars, confirming tidal interaction effects with the SMC.

Findings

Detected a significant warp in the outer LMC disk.

Constructed a high-resolution reddening map of the LMC.

Inner disk tilted relative to the outer disk.

Abstract

We present a study of the three-dimensional (3D) structure of the Large Magellanic Cloud (LMC) using ~2.2 million red clump (RC) stars selected from the Survey of the MAgellanic Stellar History. To correct for line-of-sight dust extinction, the intrinsic RC color and magnitude and their radial dependence are carefully measured by using internal nearly dust-free regions. These are then used to construct an accurate 2D reddening map (165 square degrees with ~10 arcmin resolution) of the LMC disk and the 3D spatial distribution of RC stars. An inclined disk model is fit to the 2D distance map yielding a best-fit inclination angle i = 25.86(+0.73,-1.39) degrees with random errors of +\-0.19 degrees and line-of-nodes position angle theta = 149.23(+6.43,-8.35) degrees with random errors of +/-0.49 degrees. These angles vary with galactic radius, indicating that the LMC disk is warped and twisted likely due to the repeated tidal interactions with the Small Magellanic Cloud (SMC). For the first time, our data reveal a significant warp in the southwestern part of the outer disk starting at rho ~ 7 degrees that departs from the defined LMC plane up to ~4 kpc toward the SMC, suggesting that it originated from a strong interaction with the SMC. In addition, the inner disk encompassing the off-centered bar appears to be tilted up to 5-15 degrees relative to the rest of the LMC disk. These findings on the outer warp and the tilted bar are consistent with the predictions from the Besla et al. simulation of a recent direct collision with the SMC.