Cosmic metal density evolution in neutral gas: insights from observations and cosmological simulations

We contrast the latest observations of cosmic metal density in neutral gas ($\rho_{\rm met,neu}$) with three cosmological galaxy evolution simulations: L-GALAXIES 2020, TNG100, and EAGLE. find that fraction total metals are is $<40$ per cent at $3\lesssim{} z \lesssim{} 5$ these simulations, whereas damped Lyman-$\alpha$ (DLA) systems suggest $\gtrsim{}85$ cent. In all hot, low-density also a major contributor to budget, even high redshift. By considering SFR SFR}$), HI}$), mean gas-phase metallicity ($[\langle{}{\rm M/H}\rangle{}]_{\rm neu}$), we determine two possible ways which $\rho_{\rm met,neu}$ observed DLAs redshift can be matched by (a) SFR}$ $z\gtrsim{}3$ greater than inferred from current FUV observations, or (b) high-redshift DLA samples have higher host mass overall population. If first correct, TNG100 would match ensemble data best, however there an outstanding tension between currently met,neu}$. second 2020 but require increase inside subhaloes above $z\sim{}2.5$. neither EAGLE although expense over-estimating $[\langle{}{\rm neu}$. Modulo details related numerical resolution HI modelling incompatibilities highlight tensions key properties