A relationship between stellar metallicity gradients and galaxy age in dwarf galaxies. Issue 4 (24th December 2020)

• Record Type: Journal Article
• Authors: Mercado, Francisco J; Bullock, James S; Boylan-Kolchin, Michael; Moreno, Jorge; Wetzel, Andrew; El-Badry, Kareem; Graus, Andrew S; Fitts, Alex; Hopkins, Philip F; Faucher-Giguère, Claude-André; Gurvich, Alexander B
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 501:Issue 4(2021)
• Page Start: 5121
• Page End: 5134
• Publication Date: 2020-12-24
• Subjects: galaxies: dwarf -- galaxies: formation -- cosmology: theory; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa3958
• Languages: English
• ISSNs: 0035-8711

Abstract

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 10 5.5 and 10 8.6 M⊙ . 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.