Absolute Calibration of Diffuse Radio Surveys at 45 and 150 MHz

TL;DR

This paper calibrates two diffuse radio sky maps at 45 and 150 MHz using EDGES measurements, providing correction factors and uncertainties to improve low-frequency sky models crucial for 21 cm cosmology.

Contribution

It introduces a method to determine scale and zero-level corrections for existing radio surveys using EDGES data, enhancing their accuracy for cosmological studies.

Findings

Scale correction for Guzmán et al. map: 1.076 ± 0.034

Zero-level correction for Guzmán et al. map: -160 ± 78 K

Uncertainty in corrected maps: 2.1-9.0% in brightness temperature

Abstract

We use EDGES measurements to determine scale and zero-level corrections to the diffuse radio surveys by Guzm\'an et al. at $45$ MHz and Landecker & Wielebinski at $150$ MHz. We find that the Guzm\'an et al. map requires a scale correction of $1.076 \pm 0.034$ ($2\sigma$) and a zero-level correction of $-160 \pm 78$ K ($2\sigma$) to best-fit the EDGES data. For the Landecker & Wielebinski map, the scale correction is $1.112 \pm 0.023$ ($2\sigma$) and the zero-level correction is $0.7 \pm 6.0$ K ($2\sigma$). The correction uncertainties are dominated by systematic effects, of which the most significant are uncertainty in the calibration of the EDGES receivers, antenna pointing, and tropospheric and ionospheric effects. We propagate the correction uncertainties to estimate the uncertainties in the corrected maps themselves and find that the $2\sigma$ uncertainty in the map brightness temperature is in the range $3.2-7.5\%$ for the Guzm\'an et al. map and $2.1-9.0\%$ for the Landecker & Wielebinski map, with the largest percent uncertainties occurring at high Galactic latitudes. The corrected maps could be used to improve existing diffuse low-frequency radio sky models, which are essential tools in analyses of cosmological $21$ cm observations, as well as to investigate the existence of a radio monopole excess above the cosmic microwave background and known Galactic and extragalactic contributions.