Galaxy-cluster masses via 21st-century measurements of lensing of 21-cm fluctuations

TL;DR

This paper explores the potential of using 21-cm signal lensing to measure galaxy cluster masses during the dark ages and reionization, highlighting the requirements and capabilities of future radio observations.

Contribution

It develops a quadratic estimator for cluster mass detection via 21-cm lensing and analyzes the observational tradeoffs for future radio experiments.

Findings

Dark ages lensing can detect halos >~10^12 Msun/h with futuristic setups.

EOR measurements can detect halos >~10^13 Msun/h with sufficient observation time.

Futuristic experiments are needed to overcome contamination and achieve these detections.

Abstract

We discuss the prospects to measure galaxy-cluster properties via weak lensing of 21-cm fluctuations from the dark ages and the epoch of reionization (EOR). We choose as a figure of merit the smallest cluster mass detectable through such measurements. We construct the minimum-variance quadratic estimator for the cluster mass based on lensing of 21-cm fluctuations at multiple redshifts. We discuss the tradeoff between frequency bandwidth, angular resolution, and number of redshift shells available for a fixed noise level for the radio detectors. Observations of lensing of the 21-cm background from the dark ages will be capable of detecting M>~10^12 Msun/h mass halos, but will require futuristic experiments to overcome the contaminating sources. Next-generation radio measurements of 21-cm fluctuations from the EOR will, however, have the sensitivity to detect galaxy clusters with halo masses M>~10^13 Msun/h, given enough observation time (for the relevant sky patch) and collecting area to maximize their resolution capabilities.