Reversal of Fortune: Increased Star Formation Efficiencies in the Early Histories of Dwarf Galaxies?

Abstract

On dwarf galaxy scales, the different shapes of the galaxy stellar mass function and the dark halo mass function require a star-formation efficiency (SFE) in these systems that is currently more than 1 dex lower than that of Milky Way-size halos. Here, we argue that this trend may actually be reversed at high redshift. Specifically, by combining the resolved star-formation histories of nearby isolated dwarfs with the simulated mass-growth rates of dark matter halos, we show that the assembly of these systems occurs in two phases: (1) an early, fast halo accretion phase with a rapidly deepening potential well, characterized by a high SFE; and (2) a late slow halo accretion phase where, perhaps as a consequence of reionization, the SFE is low. Nearby dwarfs have more old stars than predicted by assuming a constant or decreasing SFE with redshift, a behavior that appears to deviate qualitatively from the trends seen amongst more massive systems. Taken at face value, the data suggest that, at sufficiently early epochs, dwarf galaxy halos above the atomic cooling mass limit can be among the most efficient sites of star formation in the universe.

6 pages, 5 figures, accepted for publication in the Astrophysical Journal Letters

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Cited by in corpus (8)

• Faint dwarfs as a test of DM models: WDM vs. CDM
• Star Formation and Stellar Mass Assembly in Dark Matter Halos: From Giants to Dwarfs
• Scaling relations and baryonic cycling in local star-forming galaxies: II. Gas content and star-formation efficiency
• The Dark Energy Survey 5-year photometrically identified Type Ia Supernovae
• Star Cluster Formation and Survival in the First Galaxies
• UniverseMachine: Predicting Galaxy Star Formation over Seven Decades of Halo Mass with Zoom-in Simulations
• Scaling relations and baryonic cycling in local star-forming galaxies. III. Outflows, effective yields and metal loading factors
• The THESAN-ZOOM project: Star-formation efficiencies in high-redshift galaxies