Significant Molecular Gas Deficiencies in Star-forming Cluster Galaxies at $z\sim1.4$

TL;DR

This study reveals that star-forming galaxies in clusters at z~1.4 have significantly lower molecular gas content and shorter depletion times compared to field galaxies, indicating environment-driven gas depletion extending beyond the cluster core.

Contribution

First comprehensive stacking analysis of ALMA dust continuum data for 126 cluster galaxies at z~1.4, quantifying environmental effects on gas properties beyond the cluster core.

Findings

Cluster galaxies show 2-4x lower molecular gas masses than field galaxies.

Gas depletion timescales are 3-4x shorter in cluster galaxies.

Gas fractions are significantly reduced in cluster environments.

Abstract

We present the average gas properties derived from ALMA Band 6 dust continuum imaging of 126 massive (log $M_{\star} / M_{\odot} \gtrsim 10.5$), star-forming cluster galaxies across 11 galaxy clusters at $z=1-1.75$. Using stacking analysis on the ALMA images, combined with UV-far-infrared data, we quantify the average infrared SEDs and gas properties (molecular gas masses, $M_{\rm mol}$; gas depletion timescales, $\tau_{\rm depl}$; and gas fractions, f$_{\rm gas}$) as a function of cluster-centric radius and properties including stellar mass and distance from the Main Sequence. We find a significant dearth in the ALMA fluxes relative to that expected in the field $-$ with correspondingly low $M_{\rm mol}$ and f$_{\rm gas}$ and short $\tau_{\rm depl}$ $-$ with weak or no dependence on cluster-centric radius out to twice the virial radius. The Herschel+ALMA SEDs indicate warmer dust temperatures ($\sim36-38$ K) than coeval field galaxies ($\sim30$ K). We perform a thorough comparison of the cluster galaxy gas properties to field galaxies, finding deficits of 2-3x, 3-4x, and 2-4x in $M_{\rm mol}$, $\tau_{\rm depl}$, and f$_{\rm gas}$ compared to coeval field stacks and larger deficits compared to field scaling relations built primarily on detections. The cluster gas properties derived here are comparable with stacking analyses in (proto-)clusters in the literature and at odds with findings of field-like $\tau_{\rm depl}$ and enhanced f$_{\rm gas}$ reported using CO and dust continuum detections. Our analysis suggests that environment has considerable impact on gas properties out to large radii, in good agreement with cosmological simulations which project gas depletion begins beyond the virial radius and largely completes by first passage of the cluster core.