Selecting Sagittarius: Identification and Chemical Characterization of the Sagittarius Stream

TL;DR

This study identifies and characterizes members of the Sagittarius stream, revealing metallicity gradients and kinematic properties that inform models of the Milky Way's dark matter halo and dwarf galaxy disruption.

Contribution

It introduces a new statistical method for selecting Sagittarius stream members and provides detailed spectroscopic mapping of their metallicity and kinematics.

Findings

Identification of 106 Sagittarius stream members

Detection of a metallicity gradient in the trailing arm

High metallicity dispersion in the leading arm

Abstract

Wrapping around the Milky Way, the Sagittarius stream is the dominant substructure in the halo. Our statistical selection method has allowed us to identify 106 highly likely members of the Sagittarius stream. Spectroscopic analysis of metallicity and kinematics of all members provides us with a new mapping of the Sagittarius stream. We find correspondence between the velocity distribution of stream stars and those computed for a triaxial model of the Milky Way dark matter halo. The Sagittarius trailing arm exhibits a metallicity gradient, ranging from $-0.59$ dex to $-0.97$ dex over 142$^{\circ}$. This is consistent with the scenario of tidal disruption from a progenitor dwarf galaxy that possessed an internal metallicity gradient. We note high metallicity dispersion in the leading arm, causing a lack of detectable gradient and possibly indicating orbital phase mixing. We additionally report on a potential detection of the Sextans dwarf spheroidal in our data.