The dynamical ages of two low-luminosity young radio sources

Abstract

Context. Young radio-loud active galactic nuclei form an important tool for investigating the evolution of extragalactic radio sources. To study the early phases of expanding radio sources, we are using the CORALZ sample, which contains 25 compact ( θ< 2 �� )r adio sources associated with nearby galaxies. Aims. In this paper we aim to determine the lobe-to-lobe expansion speeds for two sources in the sample. Comparing the dynamical ages of these relatively low-luminosity objects with ages of powerful sources found in the literature, will serve to test radio source evolution models. Methods. We present our third epoch of VLBI observations, using the EVN+VLBA array at 5.0 GHz, at four and eight years after our previous measurements. Results. We report the detection of a lobe-to-lobe expansion speed of 0.095 ± 0.020 h −1 c for CORALZ J083139+460800, and a 1-σ upper limit to the expansion speed of CORALZ J131739+411545 of 0.074 h −1 c. The detected expansion speed of CORALZ J083139+460800 corresponds to a dynamical age of 245 ± 55 years. Conclusions. The detected expansion speed and upper limit are lower than any presented in the literature for powerful young AGN. This confirms that the expansion speeds of young radio sources are correlated with their radio luminosities.