J. W. Broderick, G. Drouart, N. Seymour, T. J. Galvin, N. Wright, A. Carnero Rosell, R. Chhetri, H. Dannerbauer, S. P. Driver, J. Morgan, V. A. Moss, S. Prabu, J. Afonso, C. de Breuck, B. H. C. Emonts, T. M. O. Franzen, C. M. Gutiérrez, P. Hancock, G. Heald, N. Hurley-Walker, R. J. Ivison, M. D. Lehnert, G. Noirot, M. Read, S. S. Shabala, D. Stern, W. J. Sutherland, E. Sutorius, R. J. Turner, J. Vernet
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 Ks -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 deg2 . 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∼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 Ks -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 Ks -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≳6.5 .
Keywords
galaxies: high-redshift; galaxies: active; radio continuum: galaxies; infrared: galaxies
Publications of the Astronomical Society of Australia
Volume 39
2022 November
