The imprint of bursty star formation on alpha-element abundance patterns in Milky Way-like galaxies

TL;DR

This study uses FIRE-2 simulations to show how bursty star formation history leaves a distinct chemical signature in Milky Way-like galaxies, and suggests this can be observed in stellar abundance patterns to infer galaxy evolution timelines.

Contribution

It demonstrates that bursty star formation imprints a unique chevron pattern in [Fe/H] - [O/Fe] space and proposes a method to detect the transition from bursty to steady star formation in the Milky Way.

Findings

The chevron pattern in [Fe/H] - [O/Fe] indicates past bursty star formation.

Scatter in [O/Fe] at fixed age is higher during bursty phases.

Transition to steady star formation in the Milky Way occurred 7-8 Gyr ago.

Abstract

Milky Way-mass galaxies in the FIRE-2 simulations demonstrate two main modes of star formation. At high redshifts star formation occurs in a series of short and intense bursts, while at low redshifts star formation proceeds at a steady rate with a transition from one mode to another at times ranging from 3 to 7 Gyr ago for different galaxies. We analyse how the mode of star formation affects iron and alpha-element abundance. We find that the early bursty regime imprints a measurable pattern in stellar elemental abundances in the form of a "sideways chevron" shape on the [Fe/H] - [O/Fe] plane and the scatter in [O/Fe] at a given stellar age is higher than when a galaxy is in the steady regime. That suggests that the evolution of [O/Fe] scatter with age provides an estimate of the end of the bursty phase. We investigate the feasibility of observing of this effect by adding mock observational errors to a simulated stellar survey and find that the transition between the bursty and steady phase should be detectable in the Milky Way, although larger observational uncertainties make the transition shallower. We apply our method to observations of the Milky Way from the Second APOKASC Catalog and estimate that the transition to steady star formation in the Milky Way happened 7-8 Gyrs ago, earlier than transition times measured in the simulations.