Chemical Signatures of the First Galaxies: Criteria for One-Shot Enrichment

TL;DR

This study uses metal-poor stars in ultra-faint dwarf galaxies to identify chemical signatures indicative of single, early supernova events, shedding light on the formation and feedback processes of the first galaxies.

Contribution

It develops empirical abundance criteria based on simulations to identify one-shot galaxy formation signatures in local dwarf galaxies.

Findings

Several UFDs meet the one-shot criteria, indicating early strong feedback effects.

The study links dwarf galaxy properties to the first galaxies and Milky Way formation.

Provides a new method for 'dwarf galaxy archaeology' to study early universe galaxy formation.

Abstract

We utilize metal-poor stars in the local, ultra-faint dwarf galaxies (UFDs; L_tot < 10^5 L_sun) to empirically constrain the formation process of the first galaxies. Since UFDs have much simpler star formation histories than the halo of the Milky Way, their stellar populations should preserve the fossil record of the first supernova (SN) explosions in their long-lived, low-mass stars. Guided by recent hydrodynamical simulations of first galaxy formation, we develop a set of stellar abundance signatures that characterize the nucleosynthetic history of such an early system if it was observed in the present-day universe. Specifically, we argue that the first galaxies are the product of chemical "one-shot" events, where only one (long-lived) stellar generation forms after the first, Population III, SN explosions. Our abundance criteria thus constrain the strength of negative feedback effects inside the first galaxies. We compare the stellar content of UFDs with these one-shot criteria. Several systems (Ursa Major II, and also Coma Berenices, Bootes I, Leo IV, Segue 1) largely fulfill the requirements, indicating that their high-redshift predecessors did experience strong feedback effects that shut off star formation. We term the study of the entire stellar population of a dwarf galaxy for the purpose of inferring details about the nature and origin of the first galaxies "dwarf galaxy archaeology". This will provide clues to the connection of the first galaxies, the surviving, metal-poor dwarf galaxies, and the building blocks of the Milky Way.