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

Behnam Darvish,Lu Shen,Bahram Mobasher,Christopher Martin,Tanio Diaz-Santos,Nick Z Scoville

doi:10.3847/1538-4357/aac836

Abstract

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 ∝ Δ0.03). 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) × 1011 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.

Highlights

In this paper, using large samples of galaxies covering a broad range of environments, z, M*, and specific star formation rates (sSFRs)/sSFRMS, we address the following question: Given fixed z, M*, and sSFR/sSFRMS, does the local environment affect the molecular gas content of galaxies in the local universe and at higher redshift? For the high-z sample, we rely on the Scoville et al (2017) large sample by dividing it into environmental bins
Prior to placing our sample galaxies into different density quantiles, we first fit a power-law dependence of MISM of all galaxies as a function of z, sSFR/sSFRMS, M*, and overdensity (Δ)
This seems to be at odds with some studies showing that some environmentally driven process such as ram pressure is responsible for stripping the gas and dust content of galaxies in dense environments, resulting in a lower gas mass and gas fraction than their field counterparts

Summary

Introduction

Low-z studies find a deficiency of atomic hydrogen in denser regions compared to the field (Cayatte et al 1990; Gavazzi et al 2005; Cortese et al 2011; Serra et al 2012; Catinella et al 2013; Jaffé et al 2015; Brown et al 2017). These studies along with observations of, e.g., jelly-fish galaxies in clusters (Owers et al 2012; Poggianti et al 2016) suggest that this is likely due to the ram-pressure stripping the interstellar medium of galaxies. Others find a deficit (Fumagalli et al 2009; Corbelli et al 2012; Jablonka et al 2013; Scott et al 2013; Boselli et al 2014) or even an enhancement (Mok et al 2016) of molecular gas in denser environments than the field

Results

Discussion

Conclusion