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Cosmic metal density evolution in neutral gas: insights from observations and cosmological simulations
Astrophysics of Galaxies · Submitted 14 Sep 2021
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim Modulo details related to numerical resolution and HI mass modelling in simulations, these incompatibilities highlight current tensions between key observed cosmic properties at high redshift.
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The abstract, sentence by sentence
We contrast the latest observations of the cosmic metal density in neutral gas ($\rho_{\rm met,neu}$) with three cosmological galaxy evolution simulations: L-GALAXIES 2020, TNG100, and EAGLE. We find that the fraction of total metals that are in neutral gas is $<40$ per cent at $3\lesssim{} z \lesssim{} 5$ in these simulations, whereas observations of damped Lyman-$\alpha$ (DLA) systems suggest $\gtrsim{}85$ per cent. In all three simulations, hot, low-density gas is also a major contributor to the cosmic metal budget, even at high redshift. By considering the evolution in cosmic SFR density ($\rho_{\rm SFR}$), neutral gas density ($\rho_{\rm HI}$), and mean gas-phase metallicity ($[\langle{}{\rm M/H}\rangle{}]_{\rm neu}$), we determine two possible ways in which the $\rho_{\rm met,neu}$ observed in DLAs at high redshift can be matched by simulations: (a) the $\rho_{\rm SFR}$ at $z\gtrsim{}3$ is greater than inferred from current FUV observations, or (b) current high-redshift DLA metallicity samples have a higher mean host mass than the overall galaxy population. If the first is correct, TNG100 would match the ensemble data best, however there would be an outstanding tension between the currently observed $\rho_{\rm SFR}$ and $\rho_{\rm met,neu}$. If the second is correct, L-GALAXIES 2020 would match the ensemble data best, but would require an increase in neutral gas mass inside subhaloes above $z\sim{}2.5$. If neither is correct, EAGLE would match the ensemble data best, although at the expense of over-estimating $[\langle{}{\rm M/H}\rangle{}]_{\rm neu}$. Modulo details related to numerical resolution and HI mass modelling in simulations, these incompatibilities highlight current tensions between key observed cosmic properties at high redshift.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We contrast the latest observations of the cosmic metal density in neutral gas ($\rho_{\rm met,neu}$) with three cosmological galaxy evolution simulations: L-GALAXIES 2020, TNG100, and EAGLE. | contribution 0.62 | 0.82 | 0.04 | asserted 0.93 |
| s1 | We find that the fraction of total metals that are in neutral gas is $<40$ per cent at $3\lesssim{} z \lesssim{} 5$ in these simulations, whereas observations of damped Lyman-$\alpha$ (DLA) systems suggest $\gtrsim{}85$ per cent. | result 1.00 | 0.83 | 0.52 | asserted 1.00 |
| s2 | In all three simulations, hot, low-density gas is also a major contributor to the cosmic metal budget, even at high redshift. | result 1.00 | 0.75 | 0.10 | asserted 1.00 |
| s3 | By considering the evolution in cosmic SFR density ($\rho_{\rm SFR}$), neutral gas density ($\rho_{\rm HI}$), and mean gas-phase metallicity ($[\langle{}{\rm M/H}\rangle{}]_{\rm neu}$), we determine two possible ways in which the $\rho_{\rm met,neu}$ observed in DLAs at high redshift can be matched by simulations: (a) the $\rho_{\rm SFR}$ at $z\gtrsim{}3$ is greater than inferred from current FUV observations, or (b) current high-redshift DLA metallicity samples have a higher mean host mass than the overall galaxy population. | result 0.44 | 0.92 | 0.37 | hedged possibility 0.63 |
| s4 | If the first is correct, TNG100 would match the ensemble data best, however there would be an outstanding tension between the currently observed $\rho_{\rm SFR}$ and $\rho_{\rm met,neu}$. | interpretation 0.87 | 0.74 | 0.08 | hedged possibility 0.74 |
| s5 | If the second is correct, L-GALAXIES 2020 would match the ensemble data best, but would require an increase in neutral gas mass inside subhaloes above $z\sim{}2.5$. | interpretation 0.79 | 0.77 | 0.08 | hedged possibility 0.86 |
| s6 | If neither is correct, EAGLE would match the ensemble data best, although at the expense of over-estimating $[\langle{}{\rm M/H}\rangle{}]_{\rm neu}$. | result 0.51 | 0.84 | 0.11 | hedged possibility 0.65 |
| s7 | Modulo details related to numerical resolution and HI mass modelling in simulations, these incompatibilities highlight current tensions between key observed cosmic properties at high redshift. | interpretation 0.99 | 0.56 | 0.66 | asserted 0.91 |
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The paper
Original abstract
We contrast the latest observations of the cosmic metal density in neutral gas ($\rho_{\rm met,neu}$) with three cosmological galaxy evolution simulations: L-GALAXIES 2020, TNG100, and EAGLE. We find that the fraction of total metals that are in neutral gas is $<40$ per cent at $3\lesssim{} z \lesssim{} 5$ in these simulations, whereas observations of damped Lyman-$\alpha$ (DLA) systems suggest $\gtrsim{}85$ per cent. In all three simulations, hot, low-density gas is also a major contributor to the cosmic metal budget, even at high redshift. By considering the evolution in cosmic SFR density ($\rho_{\rm SFR}$), neutral gas density ($\rho_{\rm HI}$), and mean gas-phase metallicity ($[\langle{}{\rm M/H}\rangle{}]_{\rm neu}$), we determine two possible ways in which the $\rho_{\rm met,neu}$ observed in DLAs at high redshift can be matched by simulations: (a) the $\rho_{\rm SFR}$ at $z\gtrsim{}3$ is greater than inferred from current FUV observations, or (b) current high-redshift DLA metallicity samples have a higher mean host mass than the overall galaxy population. If the first is correct, TNG100 would match the ensemble data best, however there would be an outstanding tension between the currently observed $\rho_{\rm SFR}$ and $\rho_{\rm met,neu}$. If the second is correct, L-GALAXIES 2020 would match the ensemble data best, but would require an increase in neutral gas mass inside subhaloes above $z\sim{}2.5$. If neither is correct, EAGLE would match the ensemble data best, although at the expense of over-estimating $[\langle{}{\rm M/H}\rangle{}]_{\rm neu}$. Modulo details related to numerical resolution and HI mass modelling in simulations, these incompatibilities highlight current tensions between key observed cosmic properties at high redshift.
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How the literature uses it
1 arXiv paper cite this in 2 sentences
Papers citing it
Compares with it 1 paper
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Therefore, it is expected that chemical pollution is less effective in this time frame. ii) [ref] assume different metal yields than the ones imposed on our set of simulations.
The properties of high redshift galaxies · Chemical enrichment in the simulations · 0.99
What it cites · 7 sentences without a confident label
Uses the method or tool of 1 paper
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In that study, the equilibrium Hi fraction in each gas particle is calculated by balancing the collisional and UVB photoionization rates (as parameterised by [ref] ) with the Case A recombination rate, assuming a temperature of $10^4$ K for star-forming gas and self shielding in denser regions (see [ref] ).
Modelling the uv/x-ray cosmic background with CUBA · Neutral gas density evolution · 0.84
Compares with 1 paper
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The recent analysis of [ref] , which utilises [Cii] emission line measurements and a [Cii] – Hi conversion factor calibrated to GRB host galaxies, found a similar rate of increase in $ρHI$ with redshift above $z∼2$, with this trend flattening somewhat at $z∼5-6$.
Measuring the HI content of individual galaxies out to the epoch of reionization with [CII] · Neutral gas density evolution · 0.97
Cites as background 1 paper
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The so-called “missing metals problem” was originally posed some 20 years ago by [ref] and [ref] as an order of magnitude shortfall in the co-moving density of metals which have been measured compared with those expected to have been produced by the star formation activity seen in galaxies.
Element Abundances at High Redshifts · Observational data · 0.96
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