GLEAM-300: The GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey at 300 MHz

TL;DR

GLEAM-300 adds the first wide-field 300 MHz survey of the full Southern Sky with the MWA, delivering high-fidelity mosaic images and a deep compact-source catalogue that extends spectral sampling between GLEAM and higher-frequency surveys. The work details a robust processing pipeline that handles drift-scan snapshots, grating-lobe correction, and position-dependent beam effects, culminating in 338,080 catalogue components over 217 mosaics with median resolution ~129″ and rms ~9 mJy/beam. By validating flux scales, PSF properties, and astrometry against external surveys, the study demonstrates reliable photometry and spectral energy distributions while characterizing completeness and artefact levels. The resulting dataset, including data products and cross-survey comparisons, provides critical support for SKA-Low calibration, spectral studies of diffuse and compact sources, and time-domain investigations in the 300 MHz regime.

Abstract

In this paper we present a wide-field radio survey at 300 MHz covering the sky from $-90^\circ \leq δ_\text{J2000} \lesssim +40^\circ$ using the Murchison Widefield Array (MWA). This 300-MHz survey follows the Galactic and Extragalactic All-sky MWA (GLEAM) survey, and provides an additional comparatively high-frequency data point to existing multi-frequency (72-231 MHz) data. With this data release we provide mosaic images and a catalogue of compact source components. We use two-minute snapshot observations covering 2015-2016, combining overlapping two-minute snapshot images to provide full-sensitivity mosaic images with a median root-mean-square noise of $9.1_{-2.8}^{+5.5}$ mJy beam$^{-1}$ and median angular resolution of $128.8^{\prime\prime} \times 112.5^{\prime\prime}$, with some position-dependent variation. We find a total of 338 080 unique Gaussian components across the mosaic images. The survey is the first at 300 MHz from the MWA covering the whole Southern Hemisphere. It provides a unique spectral data point that complements the existing GLEAM survey and the ongoing GLEAM-eXtended survey, and points toward results from the upcoming SKA-Low surveys.

Figures (28)

• Figure 1: Example primary beam response for a zenith pointing [declination $-26.7^\circ$, \ref{['fig:beam:m26']}] and a low-elevation pointing [declination $+18.6^\circ$, \ref{['fig:beam:p18']}]. The attenuation is displayed with square-root stretch, and the white contours trace $[0.2, 0.5, 0.9]$. The green stars indicate the main lobe, in the pointing direction, and significant grating lobes are those above the 0.2 contour.
• Figure 2: Flow diagram of the calibration procedure. The diagram shows the processing steps to assign good calibration solutions to each ObsID after initial pre-processing, and prior to peeling/outlier source subtraction, and imaging.
• Figure 3: Basic image properties per snapshot for declination strip $-55.0\hbox{$^\circ$}$. \ref{['fig:night:intpeak']}--\ref{['fig:night:intpeak2']} SNR-weighted mean $S_\text{int}/S_\text{peak}$ per snapshot after applying $f_\text{PSF}$. The dashed horizontal line is drawn at 1, and the dotted horizontal lines are drawn at a ratio difference of 20%. \ref{['fig:night:fluxratio']}--\ref{['fig:night:fluxratio2']} SNR-weighted mean flux density ratios, $S_\text{300 MHz} / S_\text{model}$, comparing to the GGSM measurement, before and after applying $f_\text{PSF}$ and $f_\text{scale}$. The horizontal lines are as in \ref{['fig:night:intpeak']}. \ref{['fig:night:rms']} median rms noise ($\sigma_\text{rms}$) per snapshot after applying the brightness scale correction factor. Dashed horizontal lines indicate 20, 50, and 100 mJy beam$^{-1}$. In \ref{['fig:night:intpeak']}--\ref{['fig:night:fluxratio2']}, the grey shaded region is drawn between $\pm1\sigma$ and in \ref{['fig:night:rms']} between the 16-th and 84-th percentiles. Snapshots are coloured by their calibration solutions. Black circles: solutions derived from a dedicated calibrator scan; red squares: nearest-in-time best solutions from other observations; blue diamonds: solutions derived from the observation itself. Note for this declination strip, only a small number of snapshots used the dedicated calibrator solutions in the first night of observing. Note the y-axis in all panels is logarithmically scaled.
• Figure 4: SNR-weighted mean $S_\text{int}/S_\text{peak}$ of sources cross-matched to the 'unresolved' RACS-SUMSS/MGPS-2 catalogue as a function of time for two example nights (top panels) and the residual ratio (bottom panels). The black points indicate SNR-weighted mean values for a given ObsID, and the red solid lines indicate fitted polynomial models to each group as described in the text and the blue dashed lines with blue markers indicate a fixed value was assigned (only relevant for the bottom panel in this case). The gray shaded regions show $\pm 1\sigma$ for each snapshot. The residuals after applying the model values are shown in the bottom panels.
• Figure 5: Models of the per-ObsID brightness scale correction factors for two example nights (top panels) and the residual ratio (bottom panels). The black points indicate weighted mean values for a given ObsID, and the red solid lines indicate fitted polynomial models to each group as described in the text. The shaded, gray regions show the weighted standard deviation. The blue dashed lines with blue markers indicate a fixed value was assigned based on the weighted mean of the individual ObsID.