Elemental Abundances in And XIX From Coadded Spectra

TL;DR

This study measures chemical abundances in Andromeda XIX using coadded spectra to understand its unusual properties and possible tidal origin, revealing higher metallicity and signs of tidal interactions.

Contribution

First measurements of [$ ext{Fe/H}$] and [$ ext{α/Fe}$] in AndXIX, providing insights into its chemical history and formation processes.

Findings

AndXIX has higher metallicity than expected for its mass.

Steep [$ ext{α/Fe}$]--[$ ext{Fe/H}$] trend suggests tidal stripping.

Evidence points to tidal interactions as key to AndXIX's evolution.

Abstract

With a luminosity similar to that of Milky Way dwarf spheroidal (dSph) systems like Sextans, but a spatial extent similar to that of ultradiffuse galaxies (UDGs), Andromeda (And) XIX is an unusual satellite of M31. To investigate the origin of this galaxy, we measure chemical abundances for AndXIX derived from medium-resolution (R$\sim$6000) spectra from Keck II/DEIMOS. We coadd 79 red giant branch stars, grouped by photometric metallicity, in order to obtain a sufficiently high signal-to-noise ratio (S/N) to measure 20 [Fe/H] and [$\alpha$/Fe] abundances via spectral synthesis. The latter are the first such measurements for AndXIX. The mean metallicity we derive for AndXIX places it $\sim2\sigma$ higher than the present-day stellar mass-metallicity relation for Local Group dwarf galaxies, potentially indicating it has experienced tidal stripping. A loss of gas and associated quenching during such a process, which prevents the extended star formation necessary to produce shallow [$\alpha$/Fe]--[Fe/H] gradients in massive systems, is also consistent with the steeply decreasing [$\alpha$/Fe]--[Fe/H] trend we observe. In combination with the diffuse structure and disturbed kinematic properties of AndXIX, this suggests tidal interactions, rather than galaxy mergers, are strong contenders for its formation.