Sailing on the Sagittarius Stream with Gaia DR2. I. The globular cluster NGC5634

TL;DR

This study uses Gaia DR2 data to confirm that the globular cluster NGC5634 is part of the Sagittarius Stream, revealing metallicity gradients and demonstrating Gaia's capability to identify stream associations without relying on disruption models.

Contribution

The paper presents a direct observational method using Gaia DR2 data to establish globular cluster associations with the Sagittarius Stream, highlighting metallicity gradients along the stream.

Findings

NGC5634 is physically associated with the Sagittarius Stream.

Multiple arms of the Stream are detected at different distances.

A metallicity gradient exists along the Stream.

Abstract

We use Gaia DR2 data to show that the globular cluster NGC5634 is physically associated with an arm of the Sagittarius Stream, the huge system of tidal tails created by the ongoing disruption of the Sagittarius dwarf spheroidal galaxy (Sgr dSph). Two additional arms of the Stream are also detected along the same line of sight, at different distances. We show that the Sgr Stream stars surrounding NGC5634 are more metal-poor, on average, than those found in the more distant Stream arm lying behind the cluster and in the main body of Sgr~dSph, confirming that a significant metallicity (and, presumably, age) gradient is present along the Stream. This analysis demonstrates the potential of the Gaia DR2 catalogue to directly verify if a cluster is physically associated to the Stream or not, without the need to rely on models of the tidal disruption of this system. [Withdrawn: see comments]