Similar Scaling Relations for the Gas Content of Galaxies Across Environments to z ∼ 3.5

Abstract

We study the effects of the local environment on the molecular gas content of a large sample of log( M * / M ⊙ ) ≳ 10 star-forming and starburst galaxies with specific star formation rates (sSFRs) on and above the main sequence (MS) to z  ∼ 3.5. ALMA observations of the dust continuum in the COSMOS field are used to estimate molecular gas masses at z  ≈ 0.5–3.5. We also use a local universe sample from the ALFALFA H i 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 Δ( M ISM  ∝ Δ 0.03 ). Similarly, gas mass fraction ( f gas ) and depletion timescale ( τ ) show no environmental dependence to z  ∼ 3.5. At  ∼ 1.8, the average , , and in densest regions is (1.6 ± 0.2) × 10 11 M ⊙ , 55 ± 2%, and 0.8 ± 0.1 Gyr, respectively, similar to those in the lowest density bin. Independent of the environment, f gas decreases and τ increases with increasing cosmic time. Cosmic molecular mass density ( ρ ) in the lowest density bins peaks at z  ∼ 1–2, and this peak happens at z  < 1 in densest bins. This differential evolution of ρ 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 ⊙ ) ≳ 10 star-forming and starburst galaxies is primarily driven by internal processes, and not by their local environment since z  ∼ 3.5.