High$-z$ [OI] emission lines: ColdSIM simulations and ALMA observations

Abstract

Neutral-oxygen [OI] far-infrared emission lines at $63\hat{I}¼$m and $145\hat{I}¼$m are powerful probes of the physical conditions in the interstellar medium, although they have not been fully exploited in high-redshift studies. We investigate the connection between [OI] emission lines and key galaxy properties, such as star formation rate (SFR) and H${}_2$ content. Our predictions are compared with existing observations and new data analysed in this work. We post-process the outputs of the ColdSIM cosmological simulations with the DESPOTIC model, taking into account [OI]$63\hat{I}¼$m self-absorption by cold foreground material. A Random Forest algorithm is employed to accelerate computations and new observational ALMA data for galaxies at redshift $z\simeq 5-7$ are used to validate our model. Our predictions show significant [OI]$63\hat{I}¼$m luminosities ($\approx 10^8{\mathrm{L}}_{\odot }$) for galaxies with SFRs of $\approx 10^2{\mathrm{M}}_{\odot }{\mathrm{yr}}^{-1}$. The $145\hat{I}¼$m line luminosity is typically $15\%$ the [OI]$63\hat{I}¼$m one and is a factor $\approx 2-20$ below high-$z$ observations. Both [OI] lines correlate with SFR and molecular mass, but exhibit flattening in scaling relations with metallicity and stellar mass. Foreground self-absorption reduces the [OI] flux by a factor of $2-4$, consistent with empirical corrections in observational studies. We find typical line ratios of [OI]$63\hat{I}¼$m / [CII]$158\hat{I}¼$m $\approx 1$ and [OI]$145\hat{I}¼$m / [CII]$158\hat{I}¼$m $\approx 0.2-$ consistent with $z\gtrsim 6$ observations, but only when [OI]$63\hat{I}¼$m self-absorption is included. Both [OI]$63\hat{I}¼$m and [OI]$145\hat{I}¼$m lines serve as tracers of star formation and molecular gas at high redshift. Their joint detection can provide constraints on the properties of the early interstellar medium and self-absorption of the [OI]$63\hat{I}¼$m line.

16 pages, 14 figures - accepted in A&A