Similar Scaling Relations for the Gas Content of Galaxies across Environments to z ~ 3.5

TL;DR

This study finds that the molecular gas content and star formation activity of massive star-forming galaxies up to redshift 3.5 are mainly influenced by internal factors, with negligible dependence on local environment across cosmic time.

Contribution

It demonstrates that galaxy molecular gas properties are largely unaffected by local environment up to z~3.5, highlighting internal processes as the primary drivers.

Findings

Molecular gas mass, gas fraction, and depletion time show no environmental dependence.

Gas properties evolve similarly across different environments over cosmic time.

Cosmic molecular mass density peaks at different redshifts depending on environment.

Abstract

We study the effects of the local environment on the molecular gas content of a large sample of log($M_{*}$/$M_{\odot}$) $\gtrsim$ 10 star-forming and starburst galaxies with specific star-formation rates (sSFRs) on and above the main sequence (MS) to $z$ $\sim$ 3.5. ALMA observations of the dust continuum in the COSMOS field are used to estimate molecular gas masses at $z$ $\approx$ 0.5-3.5. We also use a local universe sample from the ALFALFA HI survey after converting it into molecular masses. The molecular mass ($M_{ISM}$) scaling relation shows a dependence on $z$, $M_{*}$, and sSFR relative to the MS, but no dependence on environmental overdensity $\Delta$ ($M_{ISM}$ $\propto$ $\Delta^{0.03}$). Similarly, gas mass fraction (f$_{gas}$) and depletion timescale ($\tau$) show no environmental dependence to $z$ $\sim$ 3.5. At $\langle z\rangle$ $\sim$ 1.8, the average $\langle M_{ISM}\rangle$,$\langle$f$_{gas}\rangle$, and $\langle \tau \rangle$ in densest regions is (1.6$\pm$0.2)$\times$10$^{11}$ $M_{\odot}$, 55$\pm$2%, and 0.8$\pm$0.1 Gyr, respectively, similar to those in the lowest density bin. Independent of the environment, f$_{gas}$ decreases and $\tau$ increases with increasing cosmic time. Cosmic molecular mass density ($\rho$) in the lowest density bins peaks at $z$ $\sim$ 1-2, and this peak happens at $z$ $<$ 1 in densest bins. This differential evolution of $\rho$ across environments is likely due to the growth of the large-scale structure with cosmic time. Our results suggest that the molecular gas content and the subsequent star-formation activity of log($M_{*}$/$M_{\odot}$) $\gtrsim$ 10 star-forming and starburst galaxies is primarily driven by internal processes, and not by their local environment since $z$ $\sim$ 3.5.