[Paper Review] GaLactic and Extragalactic All-sky Murchison Widefield Array survey eXtended (GLEAM-X) I: Survey Description and Initial Data Release

N. Hurley‐Walker, Timothy J. Galvin+16 more|arXiv (Cornell University)|Apr 27, 2022

Radio Astronomy Observations and Technology95 references50 citations

TL;DR

This paper presents the GaLactic and Extragalactic All-sky Murchison Widefield Array survey eXtended (GLEAM-X), a deep, high-resolution low-frequency radio survey of the southern sky at 72–231 MHz using the MWA Phase II extended configuration. It delivers an initial data release of 1,447 deg² with 1.27 ± 0.15 mJy beam⁻¹ noise, cataloging 78,967 sources (98% complete at ∼50 mJy, 98.2% reliable at 5σ), enabling studies of diffuse emission, spectral indices, and transient sources.

ABSTRACT

We describe a new low-frequency wideband radio survey of the southern sky. Observations covering 72 - 231 MHz and Declinations south of $+30^\circ$ have been performed with the Murchison Widefield Array "extended" Phase II configuration over 2018 - 2020 and will be processed to form data products including continuum and polarisation images and mosaics, multi-frequency catalogues, transient search data, and ionospheric measurements. From a pilot field described in this work, we publish an initial data release covering 1,447 sq. deg over 4h < RA < 13h, -32.7deg < Dec < -20.7deg. We process twenty frequency bands sampling 72 - 231 MHz, with a resolution of $2'$ - $45"$, and produce a wideband source-finding image across 170 - 231MHz with a root-mean-square noise of $1.27\pm0.15$ mJy/beam. Source-finding yields 78,967 components, of which 71,320 are fitted spectrally. The catalogue has a completeness of 98% at $\sim50$mJy, and a reliability of 98.2% at $5\sigma$ rising to 99.7% at $7\sigma$. A catalogue is available from Vizier; images are made available on AAO Data Central, SkyView, and the PASA Datastore. This is the first in a series of data releases from the GLEAM-X survey.

Motivation & Objective

• To conduct a deep, high-resolution low-frequency radio survey of the southern sky using the upgraded Murchison Widefield Array (MWA) Phase II configuration.
• To overcome the sensitivity and resolution limitations of the original GLEAM survey by leveraging extended baselines and improved calibration.
• To produce a comprehensive data set including continuum and polarized images, multi-frequency source catalogs, transient detection products, and ionospheric measurements.
• To enable new science on diffuse radio emission, spectral aging, and low-frequency source populations, particularly in the Galactic plane and extragalactic fields.

Proposed method

• Observations were conducted from 2018–2020 using the MWA Phase II extended array configuration with maximum baselines of 5.5 km, improving angular resolution and reducing sidelobes.
• Data were processed across 20 frequency bands from 72–231 MHz, with beam resolution ranging from 2′ to 45″, using natural weighting to minimize confusion.
• Wideband source-finding imaging was performed at 170–231 MHz, achieving a root-mean-square noise of 1.27 ± 0.15 mJy beam⁻¹.
• Source extraction and spectral fitting were applied to 78,967 components, with 71,320 sources fitted spectrally using power-law and curved SED models.
• Calibration and imaging used advanced flagging, ionospheric calibration, and self-calibration techniques to minimize system effects and improve dynamic range.
• Data products were validated through completeness and reliability analysis, with 98% completeness at ∼50 mJy and 98.2% reliability at 5σ.

Experimental results

Research questions

• RQ1 What is the sensitivity, resolution, and source density of a deep, wideband low-frequency survey of the southern sky using the MWA Phase II extended array?
• RQ2 How does the improved dynamic range and reduced confusion limit of the extended MWA configuration impact source detection and flux density measurement?
• RQ3 What is the completeness and reliability of the source catalog across different flux density thresholds?
• RQ4 How do spectral indices derived from multi-frequency data inform the physical properties of radio sources, such as spectral aging or thermal emission?
• RQ5 To what extent can the survey detect diffuse radio emission and transient phenomena in the Galactic plane and extragalactic fields?

Key findings

• The initial data release covers 1,447 deg² in the right ascension range 4h ≤ RA ≤ 13h and declination range −32.7° ≤ Dec ≤ −20.7°, with a root-mean-square noise of 1.27 ± 0.15 mJy beam⁻¹ at 170–231 MHz.
• The survey detects 78,967 radio sources, of which 71,320 are spectrally fitted, with a completeness of 98% at ∼50 mJy and a reliability of 98.2% at 5σ, rising to 99.7% at 7σ.
• The improved MWA Phase II extended configuration reduces the classical confusion limit from ∼2 mJy to ∼0.3 mJy at 200 MHz, enabling deeper integration without reaching confusion limits quickly.
• The survey achieves a dynamic range improvement due to reduced sidelobe levels and better beam control, enabling more accurate flux density measurements and cleaner images.
• The source catalog includes flux densities, positions, sizes, and spectral indices across 20 frequency bands, with power-law and curved SED fits providing spectral index estimates and reduced chi-squared statistics.
• Data products, including images and the full source catalog, are publicly available via the GLEAM-X VO server and SkyView, with the catalog accessible through Vizier.