GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey II: Galactic plane 345° <l< 67°, 180° <l< 240°

Abstract

This work makes available a further 2,860 deg 2 of the GLEAM survey, covering half of the accessible Galactic Plane, across twenty frequency bands sampling 72-231 MHz, with resolution 4'-2'. Unlike previous GLEAM data releases, we used multi-scale c l e a n to better deconvolve large-scale Galactic structure. For the Galactic longitude ranges 345 • < l < 67 • , 180 • < l < 240 • , we provide a compact source catalogue of 22,037 components selected from a 60-MHz bandwidth image centred at 200-MHz, with RMS noise ≈ 10-20 mJy beam −1 and position accuracy better than 2". The catalogue has a completeness of 50 % at ≈ 120 mJy, and a reliability of 99.86 %. It covers Galactic latitudes 1 • ≤ |b| ≤ 10 • toward the Galactic Centre and |b| ≤ 10 • for other regions, and is available from Vizier; images covering |b| ≤ 10 • for all longitudes are made available on the GLEAM VO server and SkyView.

Candidate radio supernova remnants observed by the GLEAM survey over 345° <l< 60° and 180° <l< 240°

“…Low frequencies appear to offer a decided advantage in finding new SNRs over high frequencies, where both thermal and non-thermal emission have similar contributions to the Galactic brightness. Of the 49 MAGPIS candidates, 30 are in fact H II regions, while Hurley-Walker et al (2019b) show 27 new SNRs detected at low frequencies with no IR counterparts, many with pulsar associations, and Johnston-Hollitt et al (in prep.) find similar results over the region 240…”

“…The primary resource for Papers I and II is the GLEAM Galactic Plane data published by Hurley-Walker et al (2019c), which consists of 2 860 deg 2 covering 345 • < l < 60 • , 180 • < l < 240 • , and |b| ≤ 10 • . d There are 24 frequencies available: 20 × 7.68-MHz 'narrowband' images, and four 'wideband' images at frequency ranges MHz.…”

“…We therefore consider any non-central, unresolved source with a non-thermal spectrum to be a contaminating extragalactic radio source. We perform compact source-finding and fitting across the full GLEAM band as per Hurley-Walker et al (2019c), forcing the background level to match that of the surrounding SNR. Sources thus measured are then subtracted from the flux density measurements of the SNR.…”

“…The upcoming publication Su et al (in prep.) will publish the GLEAM spectra for these objects, as well as all other detected H II regions in the data release of Hurley-Walker et al (2019c).…”

“…The latest data release of this survey unveils 2 860 deg 2 of the Galactic Plane covering 345 • < l < 60 • , 180 • < l < 240 • , and |b| ≤ 10 • (Hurley-Walker et al 2019c). b This paper is the first of two papers studying SNRs in the region published by Hurley-Walker et al (2019c) and is referred to as Paper I. As the papers share common methods, datasets, and analysis, common material is presented in this paper under a single Methodology section (Section 2) and the material omitted from Paper II, the focus of which is new SNRs detected in the region.…”