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Abstract
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 > 2 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.
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.
Original language | English |
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Article number | A137 |
Pages (from-to) | 1-11 |
Number of pages | 11 |
Journal | Astronomy and Astrophysics |
Volume | 656 |
DOIs | |
Publication status | Published - 15 Dec 2021 |
Keywords / Materials (for Non-textual outputs)
- astro-ph.GA
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HIZRAD: How the monsters were made: the formation of the most massive black holes in the Universe
1/09/20 → 31/08/22
Project: Research
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Astronomy and Astrophysics at Edinburgh
Taylor, A., Best, P., Biller, B., Dunlop, J., Ivison, R., Khochfar, S., McLure, R. & Meiksin, A.
1/04/18 → 31/03/21
Project: Research