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arXiv · 2507.08787

The THESAN-ZOOM project: Mystery N/O more -- uncovering the origin of peculiar chemical abundances and a not-so-fundamental metallicity relation at $3<z<12$

William McClymont·Sandro Tacchella·Aaron Smith·Rahul Kannan·Enrico Garaldi·Ewald Puchwein·Yuki Isobe·Xihan Ji·Xuejian Shen·Zihao Wang·Vasily Belokurov·Josh Borrow·Francesco D'Eugenio·Laura Keating·Roberto Maiolino·Stephanie Monty·Mark Vogelsberger·Oliver Zier
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Abstract

We present an analysis of metallicities and chemical abundances at $3 -0.6$) 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 $\mathrm{EW}[H$\beta$]\lesssim40$ \r{A}, 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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William McClymont, Sandro Tacchella, Aaron Smith, Rahul Kannan, Enrico Garaldi, Ewald Puchwein, Yuki Isobe, Xihan Ji, Xuejian Shen, Zihao Wang, Vasily Belokurov, Josh Borrow, Francesco D'Eugenio, Laura Keating, Roberto Maiolino, Stephanie Monty, Mark Vogelsberger, Oliver Zier. 2025-07-11. The THESAN-ZOOM project: Mystery N/O more -- uncovering the origin of peculiar chemical abundances and a not-so-fundamental metallicity relation at $3<z<12$. https://arxiv.org/abs/2507.08787

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