Revisited cold gas content with atomic carbon [C I] in z=2.5 protocluster galaxies

TL;DR

This study uses atomic carbon [CI] observations to assess cold gas content in z=2.5 protocluster galaxies, comparing calibration methods and revealing environmental effects on gas depletion times.

Contribution

It demonstrates that [CI]-based gas mass estimates are consistent with CO and dust tracers in protocluster galaxies, confirming the applicability of field galaxy calibrations in dense environments.

Findings

[CI] gas measurements are comparable to CO-based estimates within calibration uncertainties.

Gas fractions in protocluster galaxies are similar to field galaxies for certain stellar masses.

Depletion times decrease more rapidly with stellar mass in protocluster galaxies, indicating earlier quenching.

Abstract

We revisit the cold gas contents of galaxies in a protocluster at z=2.49 using the lowest neutral atomic carbon transition [CI]$^3$P$_1$-$^3$P$_0$ from Atacama Large Millimeter/submillimeter Array observations. We aim to test if the same gas mass calibration applied in field galaxies can be applied to protocluster galaxies. Five galaxies out of sixteen targeted galaxies are detected in the [CI] line, and these are all previously detected in CO(3-2) and CO(4-3) and three in 1.1 mm dust continuum. We investigate the line luminosity relations between CO and [CI] in the protocluster and compare them with other previous studies. We then compare the gas mass based on three gas tracers of [CI], CO(3-2), and dust if at least one of the last two tracers are available. Using the calibration adopted for field main-sequence galaxies, the [CI]-based gas measurements are lower than or comparable to the CO-based gas measurements by -0.35 dex at the lowest with the mean deviation of -0.14 dex. The differences between [CI]- and the dust- based measurements are relatively mild by up to 0.16 dex with the mean difference of 0.02 dex. Taking these all together with calibration uncertainties, with the [CI] line, we reconfirm our previous findings that the mean gas fraction is comparable to field galaxies for a stellar-mass range of $\log(M_{\rm star}/M_\odot = [10.6, 11.3]$. However, at least for these secure five detections, the depletion time scale decreases more rapidly with stellar mass than field galaxies that might be related to earlier quenching in dense environments.