A theoretical investigation of far-infrared fine structure lines at $z>6$ and of the origin of the [OIII]88/[CII]158 enhancement

Camilla T. Nyhagen; Alice Schimek; Claudia Cicone; Davide Decataldo; Sijing Shen

doi:10.1051/0004-6361/202452718

paper

A theoretical investigation of far-infrared fine structure lines at $z > 6$ and of the origin of the [OIII]88/[CII]158 enhancement

arXiv:2410.18471 · doi:10.1051/0004-6361/202452718

Abstract

[Abridged] The [OIII] $_{88 μ m}$ /[CII] $_{158 μ m}$ and [OIII] $_{88 μ m}$ /[NII] $_{122 μ m}$ luminosity ratios have shown to be promising tracers of the ionisation state and gas-phase metallicity of the ISM. Observations of galaxies at redshift $z > 6$ show peculiarly higher [OIII] $_{88 μ m}$ /[CII] $_{158 μ m}$ luminosity ratios compared to local sources. No model has so far successfully managed to match the observed emission from both [OIII] $_{88 μ m}$ and [CII] $_{158 μ m}$ as well as their ratio. We use Cloudy to model the [CII] $_{158 μ m}$ , [OIII] $_{88 μ m}$ , [NII] $_{122 μ m}$ and [NIII] $_{57 μ m}$ emission lines of Ponos: a high-resolution ( $m_{gas} = 883.4 M_{⊙}$ ) cosmological zoom-in simulation of a galaxy at redshift $z = 6.5$ , which is post-processed using kramses-rt. We modify Carbon, Nitrogen and Oxygen abundances in our Cloudy models to obtain C/O and N/O abundance ratios respectively lower and higher than Solar, more in line with recent high-z observational constraints. We find [OIII] $_{88 μ m}$ /[CII] $_{158 μ m}$ luminosity ratios that are a factor of $\sim 5$ higher compared to models assuming solar abundances. Additionally, we find an overall better agreement of the simulation with high-z observational constraints of the [CII] $_{158 μ m}$ -SFR and [OIII] $_{88 μ m}$ -SFR relations. This shows that a lower C/O abundance ratio is essential to reproduce the enhanced [OIII] $_{88 μ m}$ /[CII] $_{158 μ m}$ luminosity ratios observed at $z > 6$ . By assuming a super-solar N/O ratio, motivated by recent $z > 6$ JWST observations, our models yield an [OIII] $_{88 μ m}$ /[NII] $_{122 μ m}$ ratio of $1.3$ , which, according to current theoretical models, would be more appropriate for a galaxy with a lower ionisation parameter than the one we estimated for Ponos.

arXiv commentAccepted for publication in Astronomy & Astrophysics. 18 pages, 14 figures

References in corpus (99)

Cited by in corpus (1)

The Baryon Budget of Galaxies across the First Billion Years

A theoretical investigation of far-infrared fine structure lines at z>6 and of the origin of the [OIII]88/[CII]158 enhancement

Abstract

References in corpus (99)

Cited by in corpus (1)

A theoretical investigation of far-infrared fine structure lines at $z > 6$ and of the origin of the [OIII]88/[CII]158 enhancement