The GLEAM 4-Jy (G4Jy) Sample: I. Definition and the catalogue

• Published in: arXiv.org
• Main Authors: White, Sarah V, Franzen, Thomas M O, Riseley, Chris J, O Ivy Wong, Kapińska, Anna D, Hurley-Walker, Natasha, Callingham, Joseph R, Thorat, Kshitij, Wu, Chen, Hancock, Paul, Hunstead, Richard W, Seymour, Nick, Swan, Jesse, Wayth, Randall, Morgan, John, Chhetri, Rajan, Jackson, Carole, Weston, Stuart, Bell, Martin, Bi-Qing, Gaensler, B M, Johnston-Hollitt, Melanie, Offringa, André, Staveley-Smith, Lister
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 21.05.2020
• Subjects: Active galactic nuclei; Algorithms; Declination; Image classification; Inspection; Machine learning; Morphology; Physics - Astrophysics of Galaxies; Radio emission; Radio jets (astronomy); Sky surveys (astronomy); Southern sky
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2004.13125

The Murchison Widefield Array (MWA) has observed the entire southern sky (Declination, \(\delta <\) 30 deg) at low radio-frequencies, over the range 72-231 MHz. These observations constitute the GaLactic and Extragalactic All-sky MWA (GLEAM) Survey, and we use the extragalactic catalogue (Galactic latitude, \(|b| >\) 10 deg) to define the GLEAM 4-Jy (G4Jy) Sample. This is a complete sample of the 'brightest' radio-sources (\(S_{\mathrm{151MHz}} >\) 4 Jy), the majority of which are active galactic nuclei with powerful radio-jets. Crucially, low-frequency observations allow the selection of such sources in an orientation-independent way (i.e. minimising the bias caused by Doppler boosting, inherent in high-frequency surveys). We then use higher-resolution radio images, and information at other wavelengths, to morphologically classify the brightest components in GLEAM. We also conduct cross-checks against the literature, and perform internal matching, in order to improve sample completeness (which is estimated to be \(>\) 95.5%). This results in a catalogue of 1,863 sources, making the G4Jy Sample over 10 times larger than that of the revised Third Cambridge Catalogue of Radio Sources (3CRR; \(S_{\mathrm{178MHz}} >\) 10.9 Jy). Of these G4Jy sources, 78 are resolved by the MWA (Phase-I) synthesised beam (\(\sim\)2 arcmin at 200 MHz), and we label 67% of the sample as 'single', 26% as 'double', 4% as 'triple', and 3% as having 'complex' morphology at \(\sim\)1 GHz (45-arcsec resolution). Alongside this, our value-added catalogue provides mid-infrared source associations (subject to 6-arcsec resolution at 3.4 micron) for the radio emission, as identified through visual inspection and thorough checks against the literature. As such, the G4Jy Sample can be used as a reliable training set for cross-identification via machine-learning algorithms. [Abstract abridged for arXiv submission.]