Simulating the Detection of the Global 21 cm Signal with MIST for Different Models of the Soil and Beam Directivity

TL;DR

This study uses simulations to evaluate how soil properties and antenna beam directivity affect the detection of the global 21 cm signal, providing guidelines for optimal observation site selection.

Contribution

It introduces electromagnetic models of soil and beam directivity to assess their impact on detecting the Cosmic Dawn signal with MIST, highlighting conditions that facilitate signal recovery.

Findings

Single-layer soil models allow straightforward signal recovery without chromaticity correction.

Two-layer soil models increase beam chromaticity, complicating signal recovery.

Certain two-layer models with specific soil properties enable recovery without correction.

Abstract

The Mapper of the IGM Spin Temperature (MIST) is a new ground-based, single-antenna, radio experiment attempting to detect the global 21 cm signal from the Dark Ages and Cosmic Dawn. A significant challenge in this measurement is the frequency-dependence, or chromaticity, of the antenna beam directivity. MIST observes with the antenna above the soil and without a metal ground plane, and the beam directivity is sensitive to the electrical characteristics of the soil. In this paper, we use simulated observations with MIST to study how the detection of the global 21 cm signal from Cosmic Dawn is affected by the soil and the MIST beam directivity. We simulate observations using electromagnetic models of the directivity computed for single- and two-layer models of the soil. We test the recovery of the Cosmic Dawn signal with and without beam chromaticity correction applied to the simulated data. We find that our single-layer soil models enable a straightforward recovery of the signal even without chromaticity correction. Two-layer models increase the beam chromaticity and make the recovery more challenging. However, for the model in which the bottom soil layer has a lower electrical conductivity than the top layer, the signal can be recovered even without chromaticity correction. For the other two-layer models, chromaticity correction is necessary for the recovery of the signal and the accuracy requirements for the soil parameters vary between models. These results will be used as a guideline to select observation sites that are favorable for the detection of the Cosmic Dawn signal.