The Structure of the Large Magellanic Halo Stellar Halo Derived Using OGLE-III RR Lyr stars

TL;DR

This study uses OGLE-III RR Lyrae stars to map the Large Magellanic Cloud's stellar halo, revealing its triaxial shape, internal reddening, and depth, with implications for understanding its structure and orientation.

Contribution

It provides the first detailed 3D model of the LMC's stellar halo using RR Lyrae stars, including shape, orientation, and extinction mapping.

Findings

The LMC's stellar halo is a triaxial ellipsoid with axes ratios 1:2.00:3.50.

The halo's longest axis is inclined by 6 degrees from the line of sight.

Stars on the Eastern side are closer than on the Western side.

Abstract

We use the recently released OGLE-III catalog of 17692 fundamental mode RR Lyr (RRab) stars in the Large Magellanic Cloud (LMC) to investigate the structure of its stellar halo. We apply conservative cuts in period, amplitude and magnitude to remove blends and other contamination. We use period--luminosity and period--color relations to determine distance and extinction of every star in our final sample of 9393 stars. In order to determine the scatter of our method, we compare the distributions of distances in two regions at the edges of the covered area with a central region. We determine the intrinsic line-of-sight dispersion in the center to be 0.135 mag or 3.21 kpc (FWHM of 0.318 mag or 7.56 kpc), assuming zero depth in one of the edge regions. The conservative cuts we apply reduce the derived depth significantly. Furthermore, we find that the distribution of RRab stars is deformed in the sense that stars on the Eastern side are closer than on the Western side. We model the RRab distribution as a triaxial ellipsoid and determine its axes ratios to be 1:2.00:3.50 with the longest axis inclined by 6 degrees from the line of sight. Another result of our analysis is an extinction map of the LMC and a map of internal reddening, which we make publicly available.