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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 and , over the redshift range . The sample is selected from the Very Large Array (VLA) FIRST 1.4-GHz radio survey over an area of sky of 2850 deg2, 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. [ABSTRACT FROM AUTHOR]

ABSTRACT We have determined the central velocity dispersions and surface brightness profiles for a sample of powerful radio galaxies in the redshift range 0.06 < z < 0.31 , which were selected on the basis of their young radio source. The optical hosts follow the fundamental plane of elliptical galaxies, showing that young radio sources reside in normal ellipticals, as do other types of radio galaxies into which these objects are believed to evolve. As young radio sources are relatively straightforward to select and the contributions of the active galactic nuclei (AGN) light to the optical spectra are minimal, these objects can readily be used to study the evolution of the fundamental plane of elliptical galaxies out to z= 1 , independent of optical selection effects. The black hole masses, M[sub bh] , of the objects in our sample have been determined using the tight empirical relation of M[sub bh] with central velocity dispersion, σ[sub e] , and for literature samples of classical radio galaxies and optically selected ellipticals. Only the optically selected inactive galaxies are found to exhibit a correlation between M[sub bh] and radio luminosity. In contrast, the radio powers of the AGN in the samples do not correlate with M[sub bh] at all, with objects at a given black hole mass ranging over seven orders of magnitude in radio power. It is unlikely that beaming of the radio emission is responsible for the range in radio powers. We have been able to tie in the local population of powerful radio sources with its parent population of inactive elliptical galaxies: the local black hole mass function has been determined using the elliptical galaxy luminosity function and the Faber–Jackson and M[sub bh]–σ relations. This was combined with the fraction of radio-loud black holes as a function of M[sub bh] , as determined from the optically selected galaxy sample, to derive the local volume-density of radio galaxies and the distribution of their black hole masses. These are shown to be consistent with the local radio luminosity function and the distribution of black hole masses as found in the radio-selected samples, and confirms that elliptical galaxies comprise the large majority of the radio-loud population of active galaxies. [ABSTRACT FROM AUTHOR]

This paper describes the selection of a new southern/equatorial sample of gigahertz peaked spectrum (GPS) radio galaxies, and subsequent optical charge-coupled device imaging and spectroscopic observations using the ESO 3.6-m telescope. The sample consists of 49 sources with -40° < δ < + 15°, b > 20° and S[sub 2.7] GHz >0.5 Jy, selected from the Parkes PKSCAT90 survey. Approximately 80 per cent of the sources are optically identified, and approximately half of the identifications have available redshifts. The R-band Hubble diagram and evolution of the host galaxies of GPS sources are reviewed. [ABSTRACT FROM AUTHOR]

This paper describes an investigation of the early evolution of extragalactic radio sources using samples of faint and bright gigahertz peaked spectrum (GPS) and compact steep spectrum (CSS) radio galaxies. Correlations found between their peak frequency, peak flux density and angular size provide strong evidence that synchrotron self-absorption is the cause of the spectral turnovers, and indicate that young radio sources evolve in a self-similar way. In addition, the data seem to suggest that the sources are in equipartition while they evolve. If GPS sources evolve to large size radio sources, their redshift dependent birth-functions should be the same. Therefore, since the lifetimes of radio sources are thought to be short compared to the Hubble time, the observed difference in redshift distribution between GPS and large size sources must be due to a difference in slope of their luminosity functions. We argue that this slope is strongly affected by the luminosity evolution of the individual sources. A scenario for the luminosity evolution is proposed in which GPS sources increase in luminosity and large-scale radio sources decrease in luminosity with time. This evolution scenario is expected for a ram-pressure confined radio source in a surrounding medium with a King profile density. In the inner parts of the King profile, the density of the medium is constant and the radio source builds up its luminosity, but after it grows large enough the density of the surrounding medium declines and the luminosity of the radio source decreases. A comparison of the local luminosity function (LLF) of GPS galaxies with that of extended sources is a good test for this evolution scenario. Unfortunately, only a handful of GPS sources are known at low redshift, and an LLF can only be derived, assuming that their cosmological number density evolution is similar to that of steep spectrum sources. The LLF derived in this way is shown to be in good agreement with the proposed evolution scenario. However, the uncertainties are large, and larger, homogeneously selected samples of GPS sources are needed. [ABSTRACT FROM AUTHOR]

We present the data and analysis of VLBI observations at 1.6, 5 and 15 GHz of a sample of faint gigahertz peaked spectrum (GPS) sources selected from the Westerbork Northern Sky Survey. The 5-GHz observations involved a global array of 16 stations and yielded data on the total sample of 47 sources. A subsample of 26 GPS sources with peak frequencies and/or peak flux densities was observed with the VLBA at 15 GHz. A second subsample of 29 sources, with was observed at 1.6 GHz using a 14-station global VLBI array. In this way, 44 of the 47 sources (94 per cent) in the sample were observed above and at or below their spectral peak. Spectral decomposition allowed us to identify three, 11, seven and two objects as compact symmetric objects, compact doubles, core–jet and complex sources, respectively. However, many of the sources classified as compact double or core–jet sources show only two components making their classification rather tentative. This may explain why the strong morphological dichotomy of GPS quasars and galaxies found for radio-bright GPS sources is not as clear in this faint sample. [ABSTRACT FROM AUTHOR]

Gigahertz Peaked Spectrum (GPS) radio galaxies are generally thought to be the young counterparts of classical extended radio sources and live in massive ellipticals. GPS sources are vital for studying the early evolution of radio-loud AGN, the trigger of their nuclear activity, and the importance of feedback in galaxy evolution. We study the Parkes half-Jansky sample of GPS radio galaxies of which now all host galaxies have been identified and 80% has their redshifts determined (0.122 < z < 1.539). Analysis of the absolute magnitudes of the GPS host galaxies show that at z > 1 they are on average a magnitude fainter than classical 3C radio galaxies. This suggests that the AGN in young radio galaxies have not yet much influenced the overall properties of the host galaxy. However their restframe UV luminosities indicate that there is a low level of excess as compared to passive evolution models. [ABSTRACT FROM PUBLISHER]