The Metallicity Gradient of Sagittarius Dwarf Spheroidal Galaxy Prior to Infall Constrained by S-PLUS Observations of its Tidal Stream

TL;DR

This study uses S-PLUS, Gaia, and APOGEE data to analyze the metallicity gradient of the Sagittarius dwarf galaxy's tidal stream, revealing a negative gradient in the progenitor and differences between its leading and trailing arms.

Contribution

It constrains the original metallicity gradient of the Sagittarius progenitor using combined photometric and spectroscopic data, demonstrating the effectiveness of photometric surveys in chemodynamical studies.

Findings

Leading arm is more metal-poor than trailing arm by 0.15--0.20 dex.

A negative metallicity gradient exists along the leading arm.

Estimated original metallicity gradient of the progenitor is between -0.38 and -0.24 dex kpc$^{-1}$.

Abstract

We study the metallicity distribution along the Sagittarius (Sgr) stream using photometric metallicities from S-PLUS DR4, combined with Gaia DR3 kinematics and APOGEE DR17 spectroscopy. Our analysis confirms that the leading arm (Galactic latitude $b > 0$) is systematically more metal-poor than the trailing arm ($b < 0$) by 0.15--0.20 dex, and reveals a clear negative metallicity gradient along the leading arm. The trailing arm shows no significant overall gradient but displays distinct inner (negative) and outer (positive) trends. These features are consistently recovered across different photometric estimators and agree with spectroscopic data. We compare these results with predictions from an $N$-body simulation, in which metallicities were assigned according to a set of imprinted radial gradients in the progenitor. We were able to constrain the original metallicity gradient of the Sgr progenitor to be between $-0.38$ and $-0.24$ dex kpc$^{-1}$ based on photometric data, and $-0.42$ to $-0.10$ dex kpc$^{-1}$ from APOGEE. These values are consistent with gradients observed in other Local Group dwarf galaxies. Our findings demonstrate that metallicity-sensitive photometric surveys such as S-PLUS are powerful tools for reconstructing the chemodynamical evolution of disrupted satellites.