Imaging the southern sky at 159 MHz using spherical harmonics with the engineering development array 2

Abstract

One of the major priorities of international radio astronomy is to study the early universe through the detection of the 21 cm HI line from the epoch of reionisation (EoR). Due to the weak nature of the 21 cm signal, an important part in the detection of the EoR is removing contaminating foregrounds from our observations as they are multiple orders of magnitude brighter. In order to achieve this, sky maps spanning a wide range of frequencies and angular scales are required for calibration and foreground subtraction. Complementing the existing low-frequency sky maps, we have constructed a Southern Sky map through spherical harmonic transit interferometry utilising the Engineering Development Array 2 (EDA2), a Square Kilometre Array (SKA) low-frequency array prototype system. We use the m-mode formalism to create an all-sky map at 159 MHz with an angular resolution of 3 degrees, with data from the EDA2 providing information over +60 degrees to –90 degrees in declination. We also introduce a new method for visualising and quantifying how the baseline distribution of an interferometer maps to the spherical harmonics and discuss how prior information can be used to constrain spherical harmonic components that the interferometer is not sensitive to.

Uncertainties of the 30-408 MHz Galactic emission as a calibration source for radio detectors in astroparticle physics

“…In the future, these difficulties can be coped with by including more and newer reference maps into the sky interpolation models and weighting them based on their inherited uncertainties. New sky surveys at MHz frequencies are on the horizon or were recently published, including direct comparisons to other maps or sky models (Eastwood et al 2018;Kriele et al 2022).…”

The AO327 Drift Survey Catalog and Data Release of Pulsar Detections

“…The latter was in turn produced by applying the power-law dependence to the sky temperature measurements at 159 MHz and the aforementioned digitized 408 MHz map. Kriele et al (2022) report an uncertainty of <0.5 K for the map of sky temperature at 159 MHz. Remazeilles et al (2015) report a zero-level uncertainty of 3 K and a calibration uncertainty of 5% for the map of sky temperature at 408 MHz.…”

“…Sky temperature generally follows a power-law dependence on observing frequency such that n µ a T t , with a typical spectral index α t ∼ −2.7 (Gervasi et al 2008). In order to estimate T sky at 327 MHz for each pulsar's position we use the 408 MHz sky temperature map of Haslam et al (1982) in its digitized version (Remazeilles et al 2015) and the spectral index map of Kriele et al (2022). The latter was in turn produced by applying the power-law dependence to the sky temperature measurements at 159 MHz and the aforementioned digitized 408 MHz map.…”

The Second Radio Synchrotron Background Workshop: Conference Summary and Report

“…Another relevant recent result is the absolute calibration computed for the Guzmán et al (2011) 45 MHz and the Landecker & Wielebinski (1970) 150 MHz all-sky maps, and soon to be computed for the Kriele et al (2022) 159 MHz map, by the EDGES collaboration using measurements from several single-dipole-antenna instruments as discussed in Section 4.18 and Monsalve et al (2021).…”

“…The results for this map are k 1 = 1.112 ± 0.023 (2σ) and k 2 = 0.7 ± 6.0 K (2σ), and the brightness temperature of the map at Galactic coordinates (l, b) = (+190°, +50°) goes from 148.9 ±  41 K in the input map to 166.3 ± 14.3 K (2σ) in the calibrated map. Currently, we are working to provide absolute calibration to the 159 MHz map recently published by Kriele et al (2022) from data obtained with the EDA2 SKA-Low prototype. For this, we are using observations with the same EDGES highand midband blade dipole antennas as for the Landecker & Wielebinski (1970) map and also observations from an earlier version of the high-band instrument, which measured with a Fourpoint antenna (Mozdzen et al 2016).…”