Kavli Affiliate: Luis C. Ho
| First 5 Authors: Xunda Sun, Xunda Sun, , ,
| Summary:
We employ the high-redshift suite of FIRE-2 cosmological hydrodynamic zoom-in
simulations to investigate the evolution of gas-phase metallicity radial
gradients in galaxies in the epoch of reionization (EoR). Our sample consists
of 22 galaxies spanning the redshift range $z sim 10-5$. We find that galaxies
at $zsim10$ exhibit a median metallicity gradient of $-0.15,mathrmdexcdot
kpc^-1$ with substantial scatter, which gradually flatten to
$-0.1,mathrmdexcdot kpc^-1$ at $zsim6$, accompanied by a reduction in
scatter. In the EoR, metallicity gradients correlate positively with stellar
mass: more massive galaxies display flatter gradients with smaller scatter,
broadly consistent with recent JWST observations. At fixed stellar mass,
galaxies with higher star formation rates (SFRs) exhibit steeper negative
gradients, while sSFR shows a strong anti-correlation with gradient slope.
Because EoR galaxies in FIRE-2 generally lack significant rotational support,
we adopt the ratio of peak-to-peak velocity shear to twice the velocity
dispersion ($Delta v/2sigma$) as a proxy for the strength of gas flows. We
find a strong positive correlation between metallicity gradients and $Delta
v/2sigma$: galaxies with lower $Delta v/2sigma$ (i.e., weaker gas flows)
tend to exhibit steeper negative gradients. Furthermore, galaxies with steeper
gradients display higher central SFR surface densities, suggesting localized
star formation with inefficient interstellar medium mixing that drives
inside-out chemical enrichment in galaxy evolution in the early Universe.
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