GaLactic and Extragalactic All-sky Murchison Widefield Array survey eXtended (GLEAM-X) III: Galactic Plane

TL;DR

This work delivers a large, low-frequency Galactic Plane continuum dataset by jointly deconvolving and mosaicking GLEAM and GLEAM-X observations with the MWA Phase II extended configuration. The approach recovers emission on a broad range of spatial scales, providing high-resolution images and a deep wideband catalogue (98,207 sources) with robust flux calibration and reliability. Spectral fitting across 20 narrow bands enables both simple and curved power-law descriptions, facilitating identification of peaked-spectrum sources and insights into Galactic structure, SNRs, H II regions, and pulsars. The release advances Galactic plane studies by improving sensitivity, astrometric accuracy, and flux reliability, enabling detailed investigations of CR electrons, GMF, and thermal/non-thermal emission across the GP.

Abstract

We present the third data release for the Galactic and Extragalactic All-Sky Murchison Widefield Array eXtended (GLEAM-X) survey, covering = 3800 deg2 of the southern Galactic Plane (GP) with \ang{233} < l < \ang{44} and |b| < \ang{11} across a frequency range of 72 - 231 MHz divided into 20 sub-bands. GLEAM-X observations were taken using the "extended" Phase-II configuration of the Murchison Widefield Array (MWA), which features baselines ranging from approximately 12 m to 5 km. This configuration limits sensitivity to the diffuse structure of the GP, with an angular resolution range of about 45'' to 2'. To achieve lower noise levels while being sensitive to a wide range of spatial scales (45''- \ang{15}), we combined these observations with the previous Galactic and Extragalactic All-Sky Murchison Widefield Array (GLEAM) survey. For the area covered, we provide images spanning the whole frequency range. A wide-band image over 170 - 231 MHz, with RMS noise of = 3 - 6 mJy/beam and source position accuracy within 1 arcseconds, is then used to perform source-finding, which yields 98,207 elements measured across 20 x 7.68 MHz frequency bands. The catalogue is 90% complete at 50 mJy within \ang{233} < l < \ang{324} and at 125 mJy in \ang{290} < l < \ang{44}, while it is 99.3% reliable overall. All the images and the catalogue are available online for download.

Figures (20)

• Figure 1: Representation of the grouping strategy for GLEAM and GLEAM-X. Each rectangle defines a group of 10--15 observations whose pointing centres fall within the coordinates of the boxed region, ensuring complete coverage over the GP across the declination range. Circular regions indicate individual fields of view, with overlaps between adjacent circles providing continuous coverage. The dashed black line marks the GP ($b = \ang{0}$) in FK5 coordinates.
• Figure 2: Flow diagram of the data reduction procedure. The diagram shows the main processing steps, from downloading the observations of each group to adding all the IDG group images to form the final mosaic.
• Figure 3: Sky coverage of the GLEAM-X survey, with the light orange region indicating the total area observed. The dark red region represents the area covered in the first data release Hurley2022, and the light red region highlights the area covered by the second data release Ross2024. In contrast, in light and dark blue are reported the area covering $\ang{290} < l < \ang{44}$ and $\ang{233} < l < \ang{324}$ respectively, presented in this data release (GP-left, GP-right). The black stars indicate the location of bright radio sources listed from left to right as they appear on the map: Hydra A, Crab, Pic A, Cygnus A, Centaurus A, and Virgo A. The black dotted line shows the GP within $|b|<\ang{10}.$
• Figure 4: The wide-bandwidth images from the data described in this paper; this illustrative figure shows the $\ang{233} < l < \ang{324}$ region. The top panel shows the 170--231 MHz. The bottom panel shows an RGB cube formed of the 72--103 MHz (R), 103--134 MHz (G), and 139--170 MHz (B) data. Dotted white lines indicate $|b| < \ang{1}$. The colour ranges used are -0.025--1.0 Jy beam$^{-1}$ and -0.095--1.25 Jy beam$^{-1}$ with an arcsinh stretch for the two panels, respectively.
• Figure 5: The wide-bandwidth images from the data described in this paper; this illustrative figure shows the $\ang{290} < l < \ang{44}$ region. The top panel shows the 170--231 MHz. The bottom panel shows an RGB cube formed of the 72--103 MHz (R), 103--134 MHz (G), and 139--170 MHz (B) data. Dotted white lines indicate $|b| < \ang{1}$. The colour ranges used are -0.025--1.0 Jy beam$^{-1}$ and -0.095--1.25 Jy beam$^{-1}$ with an arcsinh stretch for the two panels, respectively.