Brute-Force Mapmaking with Compact Interferometers: A MITEoR Northern Sky Map from 128 MHz to 175 MHz

TL;DR

This paper introduces a new interferometric imaging method suitable for large fields of view and compact arrays, successfully applied to produce a detailed northern sky map from 128 to 175 MHz, demonstrating its potential for future 21 cm cosmology experiments.

Contribution

The paper presents a novel imaging technique tailored for compact interferometers, validated with simulations and applied to real data to produce the first northern sky map in this frequency range.

Findings

First northern sky map from 128-175 MHz at 2° resolution

Spectral index of the sky measured as -2.73±0.11

Method shows promise for upcoming low-frequency arrays like HERA

Abstract

We present a new method for interferometric imaging that is ideal for the large fields of view and compact arrays common in 21 cm cosmology. We first demonstrate the method with simulations for two very different low frequency interferometers, the Murchison Widefield Array (MWA) and the MIT Epoch of Reionization (MITEoR) Experiment. We then apply the method to the MITEoR data set collected in July 2013 to obtain the first northern sky map from 128 MHz to 175 MHz at about 2 degree resolution, and find an overall spectral index of -2.73+/-0.11. The success of this imaging method bodes well for upcoming compact redundant low-frequency arrays such as HERA. Both the MITEoR interferometric data and the 150 MHz sky map are publicly available at http://space.mit.edu/home/tegmark/omniscope.html.