On the relative CNO underabundance in quasar absorption systems at $z \sim 3$ arising from Population III enrichment and attenuation by intermediate-mass black holes and primordial baryon accretion
This article uses an adapted version of the semi-analytical model of cosmic chemical enrichment developed by \citet{Corazza_2022} to reproduce the observed abundances of C, N, and O in absorption systems of quasar spectra (ASQS) at $z \gtrsim 3-6$, addressing an overproduction issue of the abovementioned elements. We address this discrepancy by updating the cosmic star formation rate (CSFR) and introducing intermediate-mass black holes (IMBHs) as permanent matter sinks without accounting for a dynamic cosmic mass accretion rate. Our results indicate that IMBHs act as essential metallicity attenuators through mass sequestration, providing the physical regulation necessary to reconcile theoretical yields with observed data. We show that the interplay between Pop III yields, the cosmic baryon accretion rate (CBAR) from primordial nucleosynthesis, and mass sequestration by IMBHs mitigates the CNO excess. This work reinforces the role of black hole-driven processes in the chemical evolution of the Universe and identifies IMBH accretion rates as a primary area for future refinement.