The CORALZ sample – I. Young radio-loud active galactic nuclei at low redshift

This paper presents a new sample of Compact Radio sources at Low Redshift (CORALZ), which is used to study the onset and evolution of young radio-loud active galactic nuclei (AGN) and their environments. The CORALZ sample consists of 28 sources, of which 17 form a ∼95 per cent statistically complete sample with S 1.4GHz >100 mJy and 0 < 2 arcsec, over the redshift range 0.005 < z < 0.16. The sample is selected from the Very Large Array (VLA) FIRST 1.4-GHz radio survey over an area of sky of 2850 deg 2 , cross-correlated with the APM Palomar Sky Survey (APM/POSS-I) catalogue. In contrast to most previous studies of young radio-loud AGN, no selection has been made on radio spectral characteristics. This is to enable investigation of the relation between radio spectra and morphologies, orientation and Doppler boosting in young radio sources, in an unbiased way. Remarkably, more than 90 per cent of the sources in the complete CORALZ sample are classified as Gigahertz Peaked Spectrum (six) or Compact Steep Spectrum (10) sources, and only one object shows indication of strong flux density variability. Several projects are under way to study this unique sample in detail, including investigation of the optical host galaxies and their emission line characteristics, radio morphologies and dynamical evolution, and the neutral hydrogen distribution and kinematics in absorption towards these strong compact radio sources.