The follow-up European VLBI Network observations of twelve GPS radio sources at 5 GHz

摘要

Aims. Gigahertz peaked spectrum (GPS) radio sources are compact extragalactic radio sources, assumed to be young radio-loud active galactic nuclei and ideal objects for studying the early evolution of extragalactic radio sources. The Very Long Baseline Interferometry (VLBI) observation with high resolution is vital for studying the structure of these compact sources. Methods.We defined a sub-sample of twelve GPS sources which have not been observed with the VLBI before, from the Parkes half-Jansky sample, and carried out VLBI observations at 1.6 GHz and 5 GHz with the European VLBI Network (EVN) in 2006 and 2008, respectively, to classify the source structure and to find compact symmetric objects (CSO_s). Additionally, we carried out the 4.85 GHz flux density observations for these sources with the Urumqi 25-m telescope between the years 2007 and 2009 to study whether there is any variability in the total flux density of the GPS sources. Results. The results of the 5 GHz VLBI observations and total flux densities of these sources are presented in this paper. From the VLBI morphologies, the spectral indices of components and the total flux variability of the twelve targets, we firmly classify three sources J0210+0419, J1135-0021, and J2058+0540 as CSO _s, and classify J1057+0012, J1203+0414, and J1600-0037 as corejet sources. The others J0323+0534, J0433-0229, J0913+1454, J1109+1043, and J1352+0232 are labelled CSO candidates, and J1352+1107 is a complex feature. Apart from core-jet sources, the total flux densities of the CSO_s and candidates are quite stable at 5 GHz both during a long-term of ～20 years relative to the PKS90 data and in a period between 2007 and 2009. The total flux densities are resolved-out by more than 20 in the 5 GHz VLBI images for 6 sources, probably because of diffuse emission. In addition, we estimated the jet viewing angles (θ) for the confirmed CSO_s by using the double-lobe flux ratio of the sources, the result being indicative of relatively large θ for the CSO_s.