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 twenty 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 $K_{\mathrm{s}}$-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 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 $K_{\mathrm{s}}$-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 $K_{\mathrm{s}}$-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 $z\gtrsim 6.5$.

49 pages, 3 figures (one of which is a multi-page figure with 102 separate panels), 9 tables, accepted for publication in PASA

References in corpus (38)

• K-corrections and filter transformations in the ultraviolet, optical, and near infrared
• The VLA Low-frequency Sky Survey
• Distant Radio Galaxies and their Environments
• The Last of FIRST: The Final Catalog and Source Identifications
• The Very Large Array Low-frequency Sky Survey Redux (VLSSr)
• The Molonglo Galactic Plane Survey (MGPS-2): Compact Source Catalogue
• Compact steep-spectrum and peaked-spectrum radio sources
• A Quick Look at the $3$GHz Radio Sky I. Source Statistics from the Very Large Array Sky Survey
• The Herschel-ATLAS Data Release 1 Paper I: Maps, Catalogues and Number Counts
• Extragalactic Peaked-Spectrum Radio Sources at Low Frequencies
• A radio spectral index map and catalogue at 147-1400 MHz covering 80 per cent of the sky
• A search for distant radio galaxies from SUMSS and NVSS: III. radio spectral energy distributions and the z-alpha correlation
• Quasars That Have Transitioned from Radio-quiet to Radio-loud on Decadal Timescales Revealed by VLASS and FIRST
• The first blazar observed at z>6
• The discovery of a highly accreting, radio-loud quasar at z=6.82
• The duty cycle of radio galaxies revealed by LOFAR: remnant and restarted radio source populations in the Lockman Hole
• RAiSE II: resolved spectral evolution in radio AGN
• On the nature of bright compact radio sources at z>4.5
• Galaxy And Mass Assembly (GAMA): The inferred mass--metallicity relation from z=0 to 3.5 via forensic SED fitting
• Delayed triggering of radio Active Galactic Nuclei in gas-rich minor mergers in the local Universe
• Interplanetary Scintillation studies with the Murchison Wide-field Array II: Properties of sub-arcsecond compact sources at low radio frequencies
• Modelling the luminosities and sizes of radio galaxies: radio luminosity function at z = 6
• Radio Detection of VIK J2318$-$3113, the Most Distant Radio-Loud Quasar ($z$=6.44)
• Imaging and Spectroscopy of Ultra Steep Spectrum Radio Sources
• Disentangling star formation and AGN activity in powerful infrared luminous radio galaxies at 1<z<4
• Resolving the Radio Emission from the Quasar P172+18 at $z=6.82$
• A new search for distant radio galaxies in the southern hemisphere - I. Sample definition and radio properties
• Spectral Variability of Radio Sources at Low Frequencies
• Caltech-NRAO Stripe 82 Survey (CNSS) Paper V: AGNs that transitioned to radio-loud state
• CHILES VERDES: Radio variability at an unprecedented depth and cadence in the COSMOS field
• Starbursts and dusty tori in distant 3CR radio galaxies
• A compact symmetric radio source born at one-tenth the current age of the Universe
• Phase Shift of Planetary Waves and Wave--Jet Resonance on Tidally Locked Planets
• Constraining the Radio Properties of the $z$=6.44 QSO VIK J2318$-$3113
• Why Do Compact Active Galactic Nuclei at High Redshift Scintillate Less?
• GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey III: South Galactic Pole data release
• A GMRT 150 MHz Search for Variables and Transients in Stripe 82
• RAiSERed: radio continuum redshifts for lobed AGNs

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