Impact of initial mass function on the chemical evolution of high-redshift galaxies

Recent observations by the James Webb Space Telescope (JWST) have found evidence for an invariant relation between stellar mass, metallicity, and star formation rate up to $z\sim 8$ and its breakdown at higher redshifts. Understanding the underlying physics driving such correlations is thus crucial. Here, we explore the impact of the initial mass function (IMF) on the chemical evolution of high-redshift galaxies. Indeed, star formation and metal enrichment in galaxies are regulated by supernova (SN) explosions and metal yields from massive stars, which are sensitive to the high-mass end of the IMF. Using the semi-analytical galaxy evolution code \textsc{a-sloth}, we follow galactic baryon cycles along merger trees built from a high-resolution cosmological simulation. Stellar feedback is modeled with up-to-date stellar evolution tracks covering the full metallicity range ($Z \sim 10^{-11} - 0.03$) and a broad stellar mass range ($m_\star\sim2 - 600\ \rm M_\odot$), including metal yields from stellar winds, core-collapse SNe, (pulsational) pair-instability SNe, and Type Ia SNe. Assuming a Kroupa-like IMF with a varying upper mass limit $m_{\max}$, we find that only models with $m_{\max} \gtrsim 200\ \rm M_\odot$ can simultaneously reproduce the observed mass-metallicity-star formation rate relation and cosmic star formation history at $z\gtrsim 4$ owing to enhanced metal yields from pair-instability SNe. Our results confirm that very massive ($\gtrsim 200\ \rm M_\odot$) stars and pair-instability SNe play an important role in the star formation and chemical enrichment histories of high-$z$ galaxies. They also have profound implications for electromagnetic transients and gravitational-wave events.