Extracting the 21 cm EoR signal using MWA drift scan data

TL;DR

This paper analyzes 55 hours of MWA drift scan data to set upper limits on the 21 cm EoR signal, demonstrating system stability and identifying promising modes for future detection efforts.

Contribution

It provides the first detailed analysis of MWA drift scan data for EoR, establishing upper limits on the HI power spectrum and assessing system stability over time.

Findings

Power spectra behave as thermal noise in the cleanest data

Upper limits on the 1D power spectrum are approximately (1000 mK)^2 at specific scales

Modes with k > 1 h Mpc^{-1} are most suitable for signal detection

Abstract

The detection of redshifted hyperfine line of neutral hydrogen (HI) is the most promising probe of the Epoch of Reionization (EoR). We report an analysis of 55 hours of Murchison Widefield Array (MWA) Phase II drift scan EoR data. The data correspond to a central frequency $\nu_0 = 154.24 \, \rm MHz$ ($z\simeq 8.2$ for the redshifted HI hyperfine line) and bandwidth $B = 10.24 \, \rm MHz$. As one expects greater system stability in a drift scan, we test the system stability by comparing the extracted power spectra from data with noise simulations and show that the power spectra for the cleanest data behave as thermal noise. We compute the HI power spectrum as a function of time in one and two dimensions. The best upper limit on the one-dimensional power spectrum are: $\Delta^2(k) \simeq (1000~\rm mK)^2$ at $k \simeq 0.2$$h~{\rm Mpc}^{-1}$ and at $k \simeq 1$$h~{\rm Mpc}^{-1}$. The cleanest modes, which might be the most suited for obtaining the optimal signal-to-noise, correspond to $k \gtrsim 1$$h~{\rm Mpc}^{-1}$. We also study the time-dependence of the foreground-dominated modes in a drift scan and compare with the expected behaviour.