Clouds, Streams and Bridges. Redrawing the blueprint of the Magellanic System with Gaia DR1

TL;DR

This paper uses Gaia DR1 data to discover stellar tidal tails and bridges around the Magellanic Clouds, revealing signs of interaction and providing insights into the structure and dynamics of the system.

Contribution

It presents the first detailed mapping of stellar tidal features around the Magellanic Clouds using Gaia DR1, including RR Lyrae and young main sequence stars, and constrains the Milky Way's gaseous corona.

Findings

Detection of stellar tidal tails extending from the LMC and SMC.

Identification of a stellar bridge between the Clouds that is offset from the gaseous bridge.

Constraints on the density of the Milky Way's hot gaseous corona.

Abstract

We present the discovery of stellar tidal tails around the Large and the Small Magellanic Clouds in the Gaia DR1 data. In between the Clouds, their tidal arms are stretched towards each other to form an almost continuous stellar bridge. Our analysis relies on the exquisite quality of the Gaia's photometric catalogue to build detailed star-count maps of the Clouds. We demonstrate that the Gaia DR1 data can be used to detect variable stars across the whole sky, and in particular, RR Lyrae stars in and around the LMC and the SMC. Additionally, we use a combination of Gaia and Gale to follow the distribution of Young Main Sequence stars in the Magellanic System. Viewed by Gaia, the Clouds show unmistakable signs of interaction. Around the LMC, clumps of RR Lyrae are observable as far as ~20 degrees, in agreement with the most recent map of Mira-like stars reported in Deason et al (2016). The SMC's outer stellar density contours show a characteristic S-shape, symptomatic of the on-set of tidal stripping. Beyond several degrees from the center of the dwarf, the Gaia RR Lyrae stars trace the Cloud's trailing arm, extending towards the LMC. This stellar tidal tail mapped with RR Lyrae is not aligned with the gaseous Magellanic Bridge, and is shifted by some ~5 degrees from the Young Main Sequence bridge. We use the offset between the bridges to put constraints on the density of the hot gaseous corona of the Milky Way.