High-redshift quasars at $z \geq 3$ -- I. Radio spectra
| Autor: | A. Erkenov, T. Semenova, N. N. Bursov, M. G. Mingaliev, V. Stolyarov, A. Kudryashova, Yu. V. Sotnikova, Alexander T. Mikhailov, R. Udovitskiy, T. V. Mufakharov |
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| Rok vydání: | 2021 |
| Předmět: |
Physics
High Energy Astrophysical Phenomena (astro-ph.HE) Spectral shape analysis Astrophysics::High Energy Astrophysical Phenomena Flux FOS: Physical sciences Astronomy and Astrophysics Quasar Astrophysics Astrophysics::Cosmology and Extragalactic Astrophysics Declination Astrophysics - Astrophysics of Galaxies Redshift Spectral line Radio telescope Space and Planetary Science Astrophysics of Galaxies (astro-ph.GA) Detection rate Astrophysics - High Energy Astrophysical Phenomena Astrophysics::Galaxy Astrophysics |
| DOI: | 10.48550/arxiv.2109.14029 |
| Popis: | We present the radio properties of optically selected quasars with $z\geq3$. The complete sample consists of 102 quasars with a flux density level $S_{1.4}\geq100$ mJy in a declination range -35$^{\circ}$ $\leq$ Dec $\leq$ +49$^{\circ}$. The observations were obtained in 2017-2020 using the radio telescope RATAN-600. We measured flux densities at six frequencies 1.2, 2.3, 4.7, 8.2, 11.2, and 22 GHz quasi-simultaneously with uncertainties of 9-31 %. The detection rate is 100, 89, and 46 % at 4.7, 11.2, and 22 GHz, respectively. We have analysed the averaged radio spectra of the quasars based on the RATAN and literature data. We classify 46 % of radio spectra as peaked-spectrum, 24 % as flat, and none as ultra-steep spectra ($\alpha\leq-1.1$). The multifrequency data reveal that a peaked spectral shape (PS) is a common feature for bright high-redshift quasars. This indicates the dominance of bright compact core emission and the insignificant contribution of extended optically thin kpc-scale components in observed radio spectra. Using these new radio data, the radio loudness $\log~R$ was estimated for 71 objects with a median value of 3.5, showing that the majority of the quasars are highly radio-loud with $\log~R>2.5$. We have not found any significant correlation between $z$ and $\alpha$. Several new megahertz-peaked spectrum (MPS) and gigahertz-peaked spectrum (GPS) candidates are suggested. Further studies of their variability and additional low-frequency observations are needed to classify them precisely. Comment: accepted for publication in MNRAS, 16 pages |
| Databáze: | OpenAIRE |
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