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Low frequency radio properties of the z>5 quasar population

Gloudemans, AJ; Duncan, KJ; Röttgering, HJA; Shimwell, TW; Venemans, BP; Best, PN; Brüggen, M; ... Williams, WL; + view all (2021) Low frequency radio properties of the z>5 quasar population. Astronomy & Astrophysics 10.1051/0004-6361/202141722. (In press). Green open access

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Optically luminous quasars at z > 5 are important probes of super-massive black hole (SMBH) formation. With new and future radio facilities, the discovery of the brightest low-frequency radio sources in this epoch would be an important new probe of cosmic reionization through 21-cm absorption experiments. In this work, we systematically study the low-frequency radio properties of a sample of 115 known spectroscopically confirmed z > 5 quasars using the second data release of the Low Frequency Array (LOFAR) Two Metre Sky survey (LoTSS-DR2), reaching noise levels of ∼80 µJy beam−1 (at 144 MHz) over an area of ∼ 5720 deg2 . We find that 41 sources (36%) are detected in LoTSS-DR2 at > 2σ significance and we explore the evolution of their radio properties (power, spectral index, and radio loudness) as a function of redshift and rest-frame ultra-violet properties. We obtain a median spectral index of −0.29+0.10 −0.09 by stacking 93 quasars using LoTSS-DR2 and Faint Images of the Radio Sky at Twenty Centimetres (FIRST) data at 1.4 GHz, in line with observations of quasars at z < 3. We compare the radio loudness of the high-z quasar sample to a lower-z quasar sample at z ∼ 2 and find that the two radio loudness distributions are consistent with no evolution, although the low number of high-z quasars means that we cannot rule out weak evolution. Furthermore, we make a first order empirical estimate of the z = 6 quasar radio luminosity function, which is used to derive the expected number of high-z sources that will be detected in the completed LoTSS survey. This work highlights the fact that new deep radio observations can be a valuable tool in selecting high-z quasar candidates for follow-up spectroscopic observations by decreasing contamination of stellar dwarfs and reducing possible selection biases introduced by strict colour cuts.

Type: Article
Title: Low frequency radio properties of the z>5 quasar population
Open access status: An open access version is available from UCL Discovery
DOI: 10.1051/0004-6361/202141722
Publisher version: https://doi.org/10.1051/0004-6361/202141722
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: Radio continuum: galaxies – quasars: general – galaxies: active – galaxies: high-redshift
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy
URI: https://discovery.ucl.ac.uk/id/eprint/10137175
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