Three-Dimensional Structure of the Magellanic System

TL;DR

This study maps the 3D structure of the Magellanic Clouds and Bridge using thousands of Cepheids and RR Lyrae stars, revealing their shapes, orientations, and the absence of a bridge connection.

Contribution

It provides the first detailed 3D structural analysis of the Magellanic System using extensive variable star data from OGLE.

Findings

LMC is mainly in the plane with a prominent bar and northern arm.

SMC has a non-planar, ellipsoidal structure extended along the line of sight.

No evidence of a bridge-like connection between the Magellanic Clouds.

Abstract

We have determined the three-dimensional structure of the Magellanic Clouds and Magellanic Bridge using over $9\,000$ Classical Cepheids (CCs) and almost $23\,000$ RR~Lyrae (RRL) stars from the fourth phase of the OGLE project. For the CCs we calculated distances based on period-luminosity relations. CCs in the LMC are situated mainly in the bar that shows no offset from the plane of the LMC. The northern arm is also very prominent with an additional smaller arm. Both are located closer to us than the entire sample. The SMC has a non-planar structure that can be described as an ellipsoid extended almost along the line of sight. We also classified nine of our CCs as Magellanic Bridge objects. These Cepheids show a large spread in three-dimensions. For the RRL stars, we calculated distances based on photometric metallicities and theoretical relations. Both Magellanic Clouds revealed a very regular structure. We fitted triaxial ellipsoids to our LMC and SMC samples. In the LMC we noticed a very prominent, non-physical blend-artifact that prevented us from analyzing the central parts of this galaxy. We do not see any evidence of a bridge-like connection between the Magellanic Clouds.