Tracing the origin of the Aquarius Stream: I

TL;DR

This study analyzes six stars of the Aquarius stream to determine its origin, finding strong evidence that it is debris from a globular cluster based on chemical signatures and stellar parameters.

Contribution

The paper provides the first detailed chemical and spectroscopic analysis confirming the globular cluster origin of the Aquarius stream.

Findings

Stars have a mean metallicity dispersion of 0.10 dex.

Aquarius stream stars cluster in globular cluster regions in chemical abundance planes.

The stream's stars are consistent with a 12 Gyr, [Fe/H] = -1.0, alpha-enhanced isochrone.

Abstract

We present an abundance analysis of six member stars of the recently discovered Aquarius stream, in an attempt to ascertain whether this halo stream is real and, if so, to understand its origin. The mean metallicities of the six stars have a dispersion of only 0.10 dex, indicating that they are part of a chemically coherent structure. We then investigate whether the stream represents the debris of a disrupted dwarf galaxy or a disrupted globular cluster. The [Ni/Fe] - [Na/Fe] plane provides a good diagnostic: globular cluster stars and dwarf spheroidal galaxy stars are well separated in this plane, and the Aquarius stream stars lie unambiguously in the globular cluster region. The Aquarius stream stars also lie on the distinct [Na/Fe] - [O/Fe] and [Mg/Fe] - [Al/Fe] relations delineated by Galactic globular cluster stars. Spectroscopic parameters for the six Aquarius stars show that they are tightly confined to a 12 Gyr, [Fe/H] = -1.0, alpha-enhanced isochrone, consistent with their identification as globular cluster debris. We present evidence that the Aquarius stream may continue through the disk and out into the northern halo. Our results indicate a globular cluster origin for the Aquarius stream, and demonstrate the potential for chemical tagging to identify the origins of Galactic substructures.