The Properties of the Magellanic Bridge Based on OGLE IV RR Lyrae Variables

TL;DR

This study uses OGLE IV RR Lyrae variables to analyze the metallicity, reddening, and distance of the Magellanic Bridge, revealing a smooth stellar transition between the Large and Small Magellanic Clouds and suggesting overlapping halo distributions.

Contribution

First detailed analysis of RR Lyrae variables in the Magellanic Bridge to determine its structure, metallicity, and distance distribution, highlighting the connection between the two galaxies.

Findings

Average metallicity [Fe/H] = -1.79 in the Bridge

Median reddening E(V-I) = 0.101

Distance modulus around 18.57 indicating stars are between the two Clouds

Abstract

We examine the properties of the Magellanic Bridge connecting the Large and Small Magellanic Clouds using ab-type RR Lyrae variables from the extensive dataset of the Optical Gravitational Lensing Experiment (OGLE), Phase IV data release. The metallicities of the RR Lyraes are determined from the characteristics of their light curves, with an average abundance of [Fe/H] = -1.790 +/- 0.011 (sem) in the Magellanic Bridge. From the individual reddenings of these stars, derived via their minimum light curve colors, we determined a median color excess of E(V-I) = 0.101 +/- 0.007 (sem) (implying E(B-V) $\approx$ 0.077). The peak distance modulus of 18.57 +/- 0.048 (sem) places the Bridge stars at distances between the two systems. The metallicity and distance distributions probe the structure of the Magellanic system as a whole, revealing a smooth transition that connects the galaxies. An examination of the HI content does not find a clear correlation between HI emission strength and RR Lyrae spatial distribution, suggesting that the old stellar populations may trace the overlapping halo distributions of the two Magellanic Clouds.