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VLBI observations of four radio quasars at z > 4: blazars or not?
Cao, H. -M.1,2; Frey, S.3; Gabanyi, K. E.3; Paragi, Z.4; Yang, J.5,6; Cseh, D.7; Hong, X. -Y.6; An, T.6,8
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Blazars are active galactic nuclei (AGN) whose relativistic jets point nearly to the line of sight. Their compact radio structure can be imaged with very long baseline interferometry (VLBI) on parsec scales. Blazars at extremely high redshifts provide a unique insight into the AGN phenomena in the early Universe. We observed four radio sources at redshift z > 4 with the European VLBI Network (EVN) at 1.7 and 5 GHz. These objects were previously classified as blazar candidates based on X-ray observations. One of them, J2134-0419 is firmly confirmed as a blazar with our VLBI observations, due to its relativistically beamed radio emission. Its radio jet extended to similar to 10 milliarcsec scale makes this source a promising target for follow-up VLBI observations to reveal any apparent proper motion. Another target, J0839+5112 shows a compact radio structure typical of quasars. There is evidence for flux density variability and its radio 'core' has a flat spectrum. However, the EVN data suggest that its emission is not Doppler-boosted. The remaining two blazar candidates (J1420+1205 and J2220+0025) show radio properties totally unexpected from radio AGN with small-inclination jet. Their emission extends to arcsec scales and the Doppler factors of the central components are well below 1. Their structures resemble that of double-lobed radio AGN with large inclination to the line of sight. This is in contrast with the blazar-type modelling of their multiband spectral energy distributions. Our work underlines the importance of high-resolution VLBI imaging in confirming the blazar nature of high-redshift radio sources.

Correspondent Emailhongmin.cao@foxmail.com (h-mc); sandor.frey@gmail.com (sf)
KeywordGalaxies: Active Galaxies: High-redshift Radio Continuum: Galaxies
WOS HeadingsScience & Technology ; Physical Sciences
Indexed BySCI
WOS KeywordActive Galactic Nuclei ; X-ray Jet ; Intrinsic Brightness Temperatures ; Spectral Energy-distributions ; Size Redshift Relation ; Sky Survey ; Distant Blazar ; Loud Quasars ; 1.4 Ghz ; Emission
WOS Research AreaAstronomy & Astrophysics
WOS SubjectAstronomy & Astrophysics
WOS IDWOS:000398418900066
Funding Organizationprogramme of the Light in China'sWestern Region(2016-QNXZ-B-21 ; National Natural Science Foundation of China(11573016 ; Hungarian National Research, Development and Innovation Office(OTKA NN110333) ; Youth Innovation Promotion Association of the Chinese Academy of Sciences (CAS) ; China-Hungary Collaboration and Exchange Programme by the International Cooperation Bureau of the CAS ; Programme for Innovative Research Team (in Science and Technology) at the University of Henan Province ; National Aeronautics and Space Administration ; EVN project(EC054) ; YBXM-2014-02) ; 11503072)
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Cited Times:6[WOS]   [WOS Record]     [Related Records in WOS]
Document Type期刊论文
Corresponding AuthorCao, H. -M.
Affiliation1.Shangqiu Normal Univ, Sch Phys & Elect Informat, 298 Wenhua Rd, Shangqiu 476000, Henan, Peoples R China
2.Chinese Acad Sci, Xinjiang Astron Observ, 150 Sci 1 St, Urumqi 830011, Xinjiang, Peoples R China
3.MTA Res Ctr Astron & Earth Sci, Konkoly Observ, POB 67, H-1525 Budapest, Hungary
4.Joint Inst VLBI ERIC, Postbus 2, NL-7990 AA Dwingeloo, Netherlands
5.Chalmers, Onsala Space Observ, Dept Earth & Space Sci, SE-43992 Onsala, Sweden
6.Chinese Acad Sci, Shanghai Astron Observ, 80 Nandan Rd, Shanghai 200030, Peoples R China
7.Radboud Univ Nijmegen, Dept Astrophys IMAPP, POB 9010, NL-6500 GL Nijmegen, Netherlands
8.Chinese Acad Sci, Key Lab Radio Astron, Nanjing 210008, Jiangsu, Peoples R China
First Author AffilicationXinjiang Astronomical Observatory, Chinese Academy of Sciences
Corresponding Author AffilicationXinjiang Astronomical Observatory, Chinese Academy of Sciences
Recommended Citation
GB/T 7714
Cao, H. -M.,Frey, S.,Gabanyi, K. E.,et al. VLBI observations of four radio quasars at z > 4: blazars or not?[J]. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY,2017,467(1):950-960.
APA Cao, H. -M..,Frey, S..,Gabanyi, K. E..,Paragi, Z..,Yang, J..,...&An, T..(2017).VLBI observations of four radio quasars at z > 4: blazars or not?.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY,467(1),950-960.
MLA Cao, H. -M.,et al."VLBI observations of four radio quasars at z > 4: blazars or not?".MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 467.1(2017):950-960.
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