Kavli Affiliate: Roberto Maiolino
| First 5 Authors: William McClymont, William McClymont, , ,
| Summary:
We present an analysis of metallicities and chemical abundances at $3<z<12$
in the THESAN-ZOOM simulations. We find that smoothly curved gas-phase and
stellar mass-metallicity relations (MZR) are already in place at $zapprox12$
and evolve slowly ($sim$0.2 dex increase for gas, $sim$0.4 dex increase for
stars at a fixed stellar mass) down to $z=3$, governed largely by the
efficiency with which galaxies retain their metals, rather than gas fraction.
The canonical fundamental metallicity relation (FMR) survives in stars but
breaks down and inverts for gas in low-mass galaxies
($M_astlesssim10^9mathrmM_odot$) due to regular dilution by
low-metallicity gas inflow. We find broad agreement of gas-phase N/O, Fe/O, and
C/O with high-redshift observations, including the presence of nitrogen-rich
galaxies (NRGs; $log(mathrmN/O)>-0.6$) without the need for exotic yields
in our chemical network. Instead, bursty star formation naturally generates
order-of-magnitude excursions in N/O on $lesssim$100 Myr timescales due to
temporally differential galactic winds; after a starburst, stellar feedback
expels gas, leaving a large population of asymptotic-giant-branch stars to
dominate the enrichment of the relatively low-mass interstellar medium. NRGs
lie below the main sequence and typically exhibit
$mathrmEW[H$beta$]lesssim40$ rA, in apparent tension with observed
high-EW NRGs. This tension is reconciled if observed NRGs are in the initial
stages of a subsequent starburst, illuminating previously enriched gas, which
is supported by the finding of high SFR surface density nitrogen-rich giant
molecular clouds.
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