A small radio galaxy at z = 4.026
Krisztina Gabányi (Konkoly Observatory Hungarian Academy of Sciences, Eötvös University)
Sándor Frey (Konkoly Observatory Hungarian Academy of Sciences)
Tao An (Shanghai Astronomical Observatory, Shanghai)
Hongmin Cao (Shangqiu Normal University)
Zsolt Paragi (Joint Institute for VLBI in Europe (JIVE))
Leonid I. Gurvits (Joint Institute for VLBI in Europe (JIVE), TU Delft - Astrodynamics & Space Missions)
Yingkang Zhang (Shanghai Astronomical Observatory, Shanghai)
Tullia Sbarrato (Istituto Nazionale di Astrofisica-Osservatorio Astronomico di Brera)
Máté Krezinger (Eötvös University, Konkoly Observatory Hungarian Academy of Sciences)
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Abstract
Less than 200 radio-loud active galactic nuclei are known above redshift 4. Around 40 of them have been observed at milliarcsecond (mas) scale resolution with very long baseline interferometry (VLBI) technique. Some of them are unresolved, compact, relativistically beamed objects, and blazars with jets pointing at small angles to the observer's line of sight. But there are also objects with no sign of relativistic beaming possibly having larger jet inclination angles. In a couple of cases, X-ray observations indicate the presence of relativistic beaming contrary to the VLBI measurements made with the European VLBI Network. J1420+1205 is a prominent example, where our 30–100 mas-scale enhanced multi element remotely linked interferometer network radio observations revealed a rich structure reminiscent of a small radio galaxy. It shows a bright hotspot that might be related to the denser interstellar medium around a young galaxy at an early cosmological epoch.