# Chemical abundances in the nucleus of the Sagittarius dwarf spheroidal galaxy

## TL;DR

This study provides detailed chemical abundance measurements for stars in the Sagittarius dwarf spheroidal galaxy's nucleus, revealing a metallicity gradient and chemical evolution insights, including the first detection of stars with [Fe/H]< -2.0.

## Contribution

It offers the largest spectroscopic sample of metallicities and alpha-element abundances for Sgr dSph stars in a specific metallicity range and introduces a chemical evolution model for the galaxy.

## Key findings

- Detected a metallicity gradient in Sgr,N population.
- First confirmed star with [Fe/H]< -2.0 in Sgr dSph.
- Reproduced chemical patterns with a high-mass progenitor model.

## Abstract

We present Iron, Magnesium, Calcium, and Titanium abundances for 235 stars in the central region of the Sagittarius dwarf spheroidal galaxy (within 9.0 arcmin ~70 pc from the center) from medium-resolution Keck/DEIMOS spectra. All the considered stars belong to the massive globular cluster M54 or to the central nucleus of the galaxy (Sgr,N). In particular we provide abundances for 109 stars with [Fe/H] > -1.0, more than doubling the available sample of spectroscopic metallicity and alpha-elements abundance estimates for Sgr dSph stars in this metallicity regime. Also, we find the first confirmed member of the Sagittarius dwarf spheroidal with [Fe/H]< -2.0 based on analysis of iron lines. We find for the first time a metallicity gradient in the Sgr,N population, whose peak iron abundance goes from [Fe/H]=-0.38 for R < 2.5 arcmin to [Fe/H]=-0.57 for 5.0 < R < 9.0 arcmin. On the other hand the trends of [Mg/Fe], [Ca/Fe], and [Ti/Fe] with [Fe/H] are the same over the entire region explored by our study. We reproduce the observed chemical patterns of the Sagittarius dwarf spheroidal as a whole with a chemical evolution model implying a high mass progenitor ( M_(DM)=6 X 10^{10} Msun ) and a significant event of mass-stripping occurred a few Gyr ago, presumably starting at the first peri-Galactic passage after infall.