Star Formation History of Draco Revealed by DESI Data Release 1: Suppressed Early Star Formation Efficiency for Milky Way Dwarf Galaxies

Abstract Dwarf galaxies serve as fossils for understanding the early star formation history (SFH) of the local Universe. In this work, we use stellar abundances for individual stars derived from the first data release (DR1) of the Dark Energy Spectroscopic Instrument (DESI) to investigate the SFH of the dwarf spheroidal galaxy Draco. We simultaneously fit the stellar metallicity distribution function (MDF) and the [Mg/Fe]–[Fe/H] trend using the galactic chemical evolution (GCE) model flexCE . Our best-fit models imply a low star formation efficiency (SFE) of 0.003–0.007 Gyr −1 , which is about 10 times lower than values reported in literature, but consistent with recent SFE estimates for ultrafaint dwarf galaxies. By combining recent literature measurements, we find that the SFEs of Milky Way dwarf galaxies scale with stellar mass as SFE ∝ M ⋆ 0.24 . A low SFE is associated with a strong outflow efficiency; we estimate a large wind mass-loading factor η wind of ≃172–260. This is well in line with the observed outflow–stellar mass relation and with the Feedback in Realistic Environment (FIRE) cosmological simulations. Our results demonstrate the power of large-scale, low- to medium-resolution stellar spectroscopic surveys to deliver robust constraints on the early formation history of galaxies in the local Universe.