The Dawning of the Stream of Aquarius in RAVE

TL;DR

This paper reports the discovery of a new nearby stellar stream in the Aquarius constellation from RAVE data, indicating a recently disrupted dwarf galaxy or globular cluster, providing insights into Galactic formation.

Contribution

It identifies a previously unknown stellar stream in the solar neighborhood and characterizes its properties and origin, expanding knowledge of Galactic halo substructures.

Findings

The stream contains 15 identified members with specific velocity and metallicity characteristics.

The stream is dynamically young, likely from a recent dwarf galaxy or globular cluster disruption.

It is a new, nearby substructure not associated with known streams.

Abstract

We identify a new, nearby (0.5 < d < 10 kpc) stream in data from the RAdial Velocity Experiment (RAVE). As the majority of stars in the stream lie in the constellation of Aquarius we name it the Aquarius Stream. We identify 15 members of the stream lying between 30 < l < 75 and -70< b <-50, with heliocentric line-of-sight velocities V_los~-200 km/s. The members are outliers in the radial velocity distribution, and the overdensity is statistically significant when compared to mock samples created with both the Besan\c{c}on Galaxy model and newly-developed code Galaxia. The metallicity distribution function and isochrone fit in the log g - T_eff plane suggest the stream consists of a 10 Gyr old population with [m/H]~-1.0. We explore relations to other streams and substructures, finding the stream cannot be identified with known structures: it is a new, nearby substructure in the Galaxy's halo. Using a simple dynamical model of a dissolving satellite galaxy we account for the localization of the stream. We find that the stream is dynamically young and therefore likely the debris of a recently disrupted dwarf galaxy or globular cluster. The Aquarius stream is thus a specimen of ongoing hierarchical Galaxy formation, rare for being right in the solar suburb.