High-resolution images of five radio quasars at early cosmological epochs
S. Frey (FOMI SGO), Z. Paragi, L.I. Gurvits (JIVE), D. Cseh (CEA SAp),, K.E. Gabanyi (FOMI SGO)

TL;DR
This study expands the high-resolution VLBI imaging of radio quasars at z>4.5, revealing their structures and physical properties, and suggests many are young, evolving objects similar to lower-redshift GPS and CSS sources.
Contribution
It nearly doubles the number of VLBI-imaged high-redshift quasars, providing new insights into their structure and evolution at early cosmic epochs.
Findings
Sources are extended but compact enough for VLBI detection.
Most have steep radio spectra, indicating non-Doppler-boosted emission.
One source shows an extended structure of ~43 kpc.
Abstract
Context: Until now, there have only been seven quasars at z>4.5 whose the high-resolution radio structure had been studied in detail with Very Long Baseline Interferometry (VLBI) imaging. Aims: We almost double the number of VLBI-imaged quasars at these high redshifts with the aim of studying their redshift-dependent structural and physical properties in a larger sample. Methods: We observed five radio quasars (J0813+3508, J1146+4037, J1242+5422, J1611+0844, and J1659+2101) at 4.5<z<5 with the European VLBI Network (EVN) at 1.6 GHz on 29 October 2008 and at 5 GHz on 22 October 2008. The angular resolution achieved ranges from 1.5 to 25 milli-arcseconds (mas), depending on the observing frequency, the position angle in the sky, and the source's celestial position. Results: The sources are all somewhat extended on mas scales, but compact enough to be detected at both frequencies. With one…
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