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 ) radio 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.

The building blocks of young AGNs: A progress report on follow‐up projects with the CORALZ sample

“…Polatidis & Conway 2003). This also confirms the upper limits derived from the first two-epoch VLBI measurements (de Vries et al 2009a). …”

“…While awaiting the results of multi-epoch measurements essential for the determination of dynamic ages (de Vries et al 2009a) a reliable alternative way to confirm the young age of these sources is the spectral aging analysis. Most of the sources show in fact significant departure from the classical power law which describes a zero age transparent synchrotron spectrum from a power law energy distribution of a relativistic electron population.…”

“…In any case for all sources in the CORALZ sample a vast range of flux densities are available for a determination of the break frequencies. With these and assuming equipartition (volumes derived from VLBI observations, de Vries et al 2009a) for the intrinsic magnetic fields, ages between 10 3 and 10 4 years are derived with J161148+404020 being the oldest source with an age less than 1.4 ×10 6 years. This is on the average at least 1000 times shorter than normally found for classical extended radio galaxies (e.g.…”

“…For the results of these observations we refer to de Vries et al (2009aVries et al ( , 2009b). An important ingredient to the structure of AGNs is the dust component, be it in form of a dusty torus or a generally dusty environment in the Interstellar Medium (ISM) around young AGNs.…”

The HI absorption “Zoo”

“…The source has a small size of LLS = 5 pc. From the lobe expansion speed analysis (de Vries et al 2010), a dynamical age of 130 yr is estimated in this source. Chandola et al (2011) detected H I absorption redshifted by +77 km s −1 relative to the systemic velocity, indicating in-falling gas towards the nuclear region.…”