Toward Empirical Constraints on the Global Redshifted 21 cm Brightness Temperature During the Epoch of Reionization

TL;DR

This paper reports initial results from a single-antenna experiment measuring the sky's radio spectrum between 100-200 MHz to constrain the 21 cm signal during reionization, setting an upper limit on brightness temperature.

Contribution

It introduces a simple, effective method to measure the all-sky spectrum and provides preliminary constraints on the epoch of reionization's timing and duration.

Findings

Placed an upper limit of 450 mK on the 21 cm brightness temperature.

Demonstrated the system's ability to reduce instrumental contaminants to 75 mK.

Outlined the potential to distinguish reionization scenarios with improved systematics.

Abstract

Preliminary results are presented from a simple, single-antenna experiment designed to measure the all-sky radio spectrum between 100 and 200 MHz. The system used an internal comparison-switching scheme to reduce non-smooth instrumental contaminants in the measured spectrum to 75 mK. From the observations, we place an initial upper limit of 450 mK on the relative brightness temperature of the redshifted 21 cm contribution to the spectrum due to neutral hydrogen in the intergalactic medium (IGM) during the epoch of reionization, assuming a rapid transition to a fully ionized IGM at a redshift of 8. With refinement, this technique should be able to distinguish between slow and fast reionization scenarios. To constrain the duration of reionization to dz > 2, the systematic residuals in the measured spectrum must be reduced to 3 mK.