A relationship between stellar metallicity gradients and galaxy age in dwarf galaxies

Francisco J. Mercado*, James S. Bullock, Michael Boylan-Kolchin, Jorge Moreno, Andrew Wetzel, Kareem El-Badry, Andrew S. Graus, Alex Fitts, Philip F. Hopkins, Claude André Faucher-Giguère, Alexander B. Gurvich

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

We explore the origin of stellar metallicity gradients in simulated and observed dwarf galaxies. We use FIRE-2 cosmological baryonic zoom-in simulations of 26 isolated galaxies as well as existing observational data for 10 Local Group dwarf galaxies. Our simulated galaxies have stellar masses between 105.5 and 108.6 MO. Whilst gas-phase metallicty gradients are generally weak in our simulated galaxies, we find that stellar metallicity gradients are common, with central regions tending to be more metal-rich than the outer parts. The strength of the gradient is correlated with galaxy-wide median stellar age, such that galaxies with younger stellar populations have flatter gradients. Stellar metallicty gradients are set by two competing processes: (1) the steady 'puffing' of old, metal-poor stars by feedback-driven potential fluctuations and (2) the accretion of extended, metal-rich gas at late times, which fuels late-time metal-rich star formation. If recent star formation dominates, then extended, metal-rich star formation washes out pre-existing gradients from the 'puffing' process. We use published results from ten Local Group dwarf galaxies to show that a similar relationship between age and stellar metallicity-gradient strength exists among real dwarfs. This suggests that observed stellar metallicity gradients may be driven largely by the baryon/feedback cycle rather than by external environmental effects.

Original languageEnglish (US)
Pages (from-to)5121-5134
Number of pages14
JournalMonthly Notices of the Royal Astronomical Society
Volume501
Issue number4
DOIs
StatePublished - Mar 1 2021

Keywords

  • cosmology: theory
  • galaxies: dwarf
  • galaxies: formation

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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