The GLEAMing of the first supermassive black holes: II. A new sample of high-redshift radio galaxy candidates. (28th November 2022)

• Record Type: Journal Article
• Authors: Broderick, J. W.; Drouart, G.; Seymour, N.; Galvin, T. J.; Wright, N.; Carnero Rosell, A.; Chhetri, R.; Dannerbauer, H.; Driver, S. P.; Morgan, J. S.; Moss, V. A.; Prabu, S.; Afonso, J. M.; De Breuck, C.; Emonts, B. H. C.; Franzen, T. M. O.; Gutiérrez, C. M.; Hancock, P. J.; Heald, G. H.; Hurley-Walker, N.; Ivison, R. J.; Lehnert, M. D.; Noirot, G.; Read, M.; Shabala, S. S.; Stern, D.; Sutherland, W. J.; Sutorius, E.; Turner, R. J.; Vernet, J.
• Is Part Of: Publications of the Astronomical Society of Australia. Volume 39(2022)
• Publication Date: 2022-11-28
• Subjects: galaxies: high-redshift -- galaxies: active -- radio continuum: galaxies -- infrared: galaxies; Astronomy -- Periodicals; Southern sky (Astronomy) -- Periodicals; Astrophysics -- Periodicals; Periodicals; 520.5
• DOI: 10.1017/pasa.2022.42
• Languages: English
• ISSNs: 1323-3580

Abstract

Abstract: While unobscured and radio-quiet active galactic nuclei are regularly being found at redshifts $z > 6$, their obscured and radio-loud counterparts remain elusive. We build upon our successful pilot study, presenting a new sample of low-frequency-selected candidate high-redshift radio galaxies (HzRGs) over a sky area 20 times larger. We have refined our selection technique, in which we select sources with curved radio spectra between 72–231 MHz from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. In combination with the requirements that our GLEAM-selected HzRG candidates have compact radio morphologies and be undetected in near-infrared $K_{\rm s}$ -band imaging from the Visible and Infrared Survey Telescope for Astronomy Kilo-degree Infrared Galaxy (VIKING) survey, we find 51 new candidate HzRGs over a sky area of approximately $1200\ \mathrm{deg}^2$ . Our sample also includes two sources from the pilot study: the second-most distant radio galaxy currently known, at $z=5.55$, with another source potentially at $z \sim 8$ . We present our refined selection technique and analyse the properties of the sample. We model the broadband radio spectra between 74 MHz and 9 GHz by supplementing the GLEAM data with both publicly available data and new observations from the Australia Telescope Compact Array at 5.5 and 9 GHz. In addition, deep $K_{\rm s}$ -band imaging from the High-Acuity Widefield K -band Imager (HAWK-I) on the Very Large Telescope and from the Southern Herschel Astrophysical Terahertz Large Area Survey Regions $K_{\rm s}$ -band Survey (SHARKS) is presented for five sources. We discuss the prospects of finding very distant radio galaxies in our sample, potentially within the epoch of reionisation at $z \gtrsim 6.5$ .