Star formation history of Draco revealed by DESI DR1: suppressed early star formation efficiency for Milky Way dwarf galaxies

Dwarf galaxies serve as fossils for understanding the early star formation history of the local Universe. In this work, we use stellar abundances for individual stars derived from the first data release of the Dark Energy Spectroscopic Instrument (DESI DR1) to investigate the star formation history 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 to 0.007, Gyr-1, which is about ten times lower than values reported in the literature, but consistent with recent SFE estimates for ultra-faint dwarf galaxies. By combining recent literature measurements, we find that the SFEs of Milky Way dwarf galaxies scale with stellar mass as SFE proportional to M 0.24. A low star formation efficiency is associated with a strong outflow efficiency; we estimate a large wind mass-loading factor η wind of approximately 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.