Tight correlation of star formation with [Ci] and CO lines across cosmic time

TL;DR

This study systematically analyzes the relationship between molecular gas tracers [CI] and CO lines and star formation rates across cosmic time, revealing consistent correlations and calibrations that suggest stable star formation relations over different epochs.

Contribution

It provides a comprehensive, multi-scale analysis of [CI] and CO line luminosities as tracers of star formation, with new calibrations and evidence of their stable relation across cosmic history.

Findings

[CI] and CO trace similar molecular gas content.

Star formation relations show little evolution over cosmic time.

Derived calibration factors for molecular mass tracers.

Abstract

Context. Cold molecular gas tracers, such as CI and CO lines, have been widely used to infer specific characteristics of the ISM and to derive star-formation relations among galaxies. Aims. However, there is still a lack of systematic studies of the star-formation scaling relation of CO and [CI] lines across cosmic time on multiple physical scales. Methods. We used observations of the ground state transitions of [CI], CO, and [CII], for 885 sources collected from the literature, to infer possible correlations between line luminosities of $\rm L^{'}_{[CI](1-0)}, \rm L^{'}_{CO(1-0)}$, and $\rm L^{'}_{[CII]}$ with star formation rates (SFR). With linear regression, we fit the relations between SFR and molecular mass derived from CO, CI, and CII lines. Results. The relation between [CI] and CO-based total molecular masses is weakly superlinear. Nevertheless, they can be calibrated against each other. For $\rm \alpha_{CO} = 0.8$ and $4.0\ \rm {M}_{\odot}\,({K}\,{km}\,{s}^{-1}\,{pc}^2)^{-1}$ we derive $\alpha_{\rm [CI]} = 3.9$ and $\sim$$17\ \rm {M}_{\odot}\,({K}\,{km}\,{s}^{-1}\,{pc}^2)^{-1}$ , respectively. Using the \emph{lmfit} package, we derived relation slopes of SFR--$\rm L^{'}_{[CI](1-0)}$, SFR--$\rm L^{'}_{CO(1-0)}$, and SFR--$\rm L^{'}_{[CII](1-0)}$ to be $\rm \beta$ = 1.06 $\pm$ 0.02, 1.24 $\pm$ 0.02, and 0.74 $\pm$ 0.02, respectively. With a Bayesian-inference \emph{linmix} method, we find consistent results. Conclusions. Our relations for [CI](1-0) and CO(1-0) indicate that they trace similar molecular gas contents, across different redshifts and different types of galaxies. This suggests that these correlations do not have strong evolution with cosmic time.