# Astro2020 Science White Paper: The Extended Cool Gas Reservoirs Within z > 1 (Proto-)Cluster Environments

## TL;DR

This paper emphasizes the importance of large radio/millimeter telescopes like the GBT in studying cold gas in high-redshift proto-clusters, crucial for understanding galaxy formation and evolution.

## Contribution

It highlights the role of large single-dish radio telescopes in constraining cold gas content in proto-clusters, supporting future high-resolution interferometric observations.

## Key findings

- Large single-dish telescopes provide essential short-spacing data.
- Combined observations improve total baryonic mass estimates.
- High-sensitivity measurements reveal low-surface brightness gas.

## Abstract

High-redshift ($z$) proto-clusters will serve as testing grounds to probe the gas supply furnishing the emerging metals, stars, and large-scale structures we see at the current epoch. This work focuses on the major role large radio/millimeter (mm) single dish facilities will have in constraining the bulk, cold (T $= 10^{1-4}$K) molecular and atomic gas content. To highlight the need for large radio/mm single dishes, we calculate how the high-sensitivity of the Green Bank Telescope's (GBT) unblocked 100m aperture provides vital interferometric short-spacing coverage to support higher-resolution ngVLA observations of the cold neutral gas at the largest scales. These combined observations are optimal for revealing low-surface brightness emission, and thus aid in the total baryonic mass estimates across cosmic time.