The GLEAMing of the first supermassive black holes: II. A new sample of high-redshift radio galaxy candidates
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 WidefieldK-band Imager (HAWK-I) on the Very Large Telescope and from the SouthernHerschelAstrophysical 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$z \gtrsim 6.5$.
- Publication:
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Publications of the Astronomical Society of Australia
- Pub Date:
- April 2022
- DOI:
- 10.1017/pasa.2022.42
- arXiv:
- arXiv:2204.08490
- Bibcode:
- 2022PASA...39...61B
- Keywords:
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- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 49 pages, 3 figures (one of which is a multi-page figure with 102 separate panels), 9 tables, accepted for publication in PASA