The metallicity distribution in the core of the Sagittarus dwarf spheroidal: minimising the metallicity biases

TL;DR

This study provides the first metallicity distribution of the Sagittarius dwarf spheroidal galaxy's core, carefully selected to minimize biases, revealing a narrow peak around [Fe/H]~-0.5 and correlations with kinematic properties.

Contribution

It presents a bias-minimized, high-resolution metallicity and velocity dataset for Sgr dSph core, offering new insights into its chemical and dynamical structure.

Findings

Metallicity ranges from [Fe/H]~-2.3 to 0.0.

Distribution peaks around [Fe/H]~-0.5.

Stars with higher metallicity show lower velocity dispersion.

Abstract

We present metallicity and radial velocity for 450 bonafide members of the Sagittarius dwarf spheroidal (Sgr dSph) galaxy, measured from high resolution (R~18000) FLAMES@VLT spectra. The targets were carefully selected (a) to sample the core of the main body of Sgr dSph while avoiding contamination from the central stellar nucleus, and (b) to prevent any bias on the metallicity distribution, by selecting targets based on their Gaia parallax and proper motions. All the targets selected in this way were confirmed as radial velocity members. We used this sample to derive the first metallicity distribution of the core of the Sgr dSph virtually unaffected by metallicity biases. The observed distribution ranges from [Fe/H]~ -2.3 to [Fe/H]~ 0.0, with a strong, symmetric and relatively narrow peak around [Fe/H]~ -0.5 and a weak, extended metal-poor tail, with only 13.8 +/- 1.9% of the stars having [Fe/H]< -1.0. We confirm previous evidence of correlations between chemical and kinematical properties of stars in the core of Sgr. In our sample stars with [Fe/H]>= -0.6 display a lower velocity dispersion and a higher rotation amplitude than those with [Fe/H]< -0.6, confirming previous suggestions of a disk/halo structure for the progenitor of the system.