Radio interferometric observations of two core-dominated triple radio sources atz > 3

¹ Laboratoire Astrophysique des Interactions Multi-echelles (UMR 7158), CEA/DSM-CNRS-Université Paris Diderot, CEA Saclay, 91191 Gif-sur-Yvette, France
e-mail: david.cseh@cea.fr
² FÖMI Satellite Geodetic Observatory, PO Box 585, 1592 Budapest, Hungary
e-mail: frey@sgo.fomi.hu; gabanyik@sgo.fomi.hu
³ Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, The Netherlands
e-mail: zparagi@jive.nl; lgurvits@jive.nl
⁴ MTA Research Group for Physical Geodesy and Geodynamics, PO Box 91, 1521 Budapest, Hungary
⁵ Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai Chuo-ku, Kanagawa, Sagamihara 252-5210, Japan

Received: 3 June 2010
Accepted: 5 August 2010

Abstract

Aims. We selected two radio quasars (J1036+1326 and J1353+5725) based on their 1.4-GHz radio structure, which is dominated by a bright central core and a pair of weaker and nearly symmetric lobes at  ~10″ angular separation. They are optically identified in the Sloan Digital Sky Survey (SDSS) at spectroscopic redshifts z > 3. We investigate the possibility that their core-dominated triple morphology can be a sign of restarted radio activity in these quasars, involving a significant repositioning of the radio jet axis.

Methods. We present the results of high-resolution radio imaging observations of J1036+1326 and J1353+5725, performed with the European Very Long Baseline Interferometry (VLBI) Network (EVN) at 1.6 GHz. These data are supplemented by archive observations from the Very Large Array (VLA). We study the large- and small-scale radio structures and the brightness temperatures, then estimate relativistic beaming parameters.

Results. We show that the central emission region of these two high-redshift, core-dominated triple sources is compact but resolved at  ~10 milli-arcsecond resolution. We find that it is not necessary to invoke large misalignment between the VLBI jet and the large-scale radio structure to explain the observed properties of the sources.