The Apache Point Observatory extra-Galactic Evolution Experiment (APOeGEE): Chemical Abundance Trends for Seven Dwarf Spheroidal Galaxies in the APOGEE Survey

TL;DR

This study analyzes chemical abundance patterns in seven dwarf spheroidal galaxies using APOGEE data, revealing their star formation histories and their limited contribution to the Milky Way halo.

Contribution

It introduces a novel method to determine measurable chemical abundance limits in APOGEE spectra and compares these patterns across multiple dwarf galaxies.

Findings

Most galaxies have distinct abundance patterns from MW halo stars.

Dwarf galaxies follow episodic or continuous star formation paths.

Proximity to larger galaxies influences their star formation history.

Abstract

In addition to comprehensive surveys of the Milky Way bulge, disk, and halo, the Apache Point Galactic Evolution Experiment (APOGEE) project observed seven dwarf spheroidal satellites (dSphs) of the Milky Way: Carina, Sextans, Sculptor, Draco, Ursa Minor, Bootes 1, and Fornax. APOGEE radial velocities, stellar parameters, and Gaia EDR3 proper motions are used to identify member stars in the vicinity of each dwarf. To properly analyze the abundance patterns of these galaxies, a novel procedure was developed to determine the measurable upper limits of the APOGEE chemical abundances as a function of the effective temperature and the spectral signal-to-noise ratio. In general, the APOGEE abundance patterns of these galaxies (limited to [Fe/H] $>$ -2.5) agree with those found in high-resolution optical studies after abundance offsets are applied. Most of the galaxies studied have abundance patterns that are distinctly different from the majority of stars found in the MW halo, suggesting that these galaxies contributed little to the MW halo above [Fe/H] $>$ -2.0. From these abundance patterns, we find that these dSphs tend to follow two types of chemical evolution paths: episodic and continuous star formation, a result that is consistent with previous photometric studies of their star formation histories. We explore whether mass and/or environment have an impact on whether a galaxy has an episodic or continuous star formation history, finding evidence that, in addition to the galaxy's mass, proximity to a larger galaxy and the cessation of star formation may drive the overall shape of the chemical evolution.