Chemical Abundances in our Ultra-Faint Dwarf Galaxies: Hydrus I and Willman 1

The Early Universe continues to be largely elusive — with many questions unanswered involving the origins, evolutionary histories, and compositional characteristics of the smallest, most ancient galaxies — ultra–faint dwarfs (UFDs). While the counts and kinematics of observed UFDs are roughly accommodated in simulations and semi-analytical models, reproducing their metallicities has remained a persistent tension between observations and theory. Simulations predict a strong scaling between M∗ and [Fe/H] that is understood as a result of star formation proceeding mostly in-situ and polluting the interstellar medium proportionally to the number of stars formed. Instead, observations suggest that there is a "flattening" or plateau on the scale of ultrafaints, hinting at a decoupling between the stellar mass and the amount of metals produced. This disagreement has profound implications: Are UFDs just tidally stripped remnants of more massive galaxies? Is there a minimum mass threshold for galaxy formation? Are many ultrafaints actually stellar clusters, indicating a lack of understanding of dark matter halo occupation fractions? Metallicity and detailed chemical abundance measurements can assist in sorting these possibilities. Here I will present work in progress detailing the chemical abundances in 2 ultrafaint dwarf galaxies in the metallicity plateau: Hydrus I and Willman 1.