The goal of this work is to determine the nature of the relation between morphology and accretion mode in radio galaxies, including environmental parameters. The CoNFIG extended catalogue (improved by new K S -band identifications and estimated redshifts from UKIDSS, and spectral index measurements from new GMRT observations) is used to select a sub-sample of 206 radio galaxies with z 0.3 over a wide range of radio luminosity, which are morphology-classified using the Fanaroff-Riley (FR) classification of extended radio sources. For each galaxy, spectroscopic data are retrieved to determine the high/low excitation status of the source, related to its accretion mode. Environmental factors, such as the host galaxy luminosity and a richness factor are also computed, generally using SDSS data. We find the following results: (1) At a given radio luminosity, the FR morphological split of sources is consistent with being the same for both accretion modes. This remains true if analysis is restricted to only rich or only poor environments. If confirmed with a larger sample, this would imply that extended radio morphology is independent of the accretion mode of the black hole, depending only on the power of the resultant jet, and its interactions with the larger-scale environment. (2) Excitation modes seem to be linked to the source environment, with high-excitation galaxies found almost exclusively in low-density environments while low-excitation galaxies occupy a wider range of densities; this result is independent of FR morphology, and is consistent with the different fuelling mechanisms expected for these excitation modes.(3) Independent of excitation mode, FRI sources are found to lie in higher density environments, on average, than FRII sources, consistent with FRI sources having their jets disrupted by a denser surrounding medium. However, there is a significant overlap in environment between the two classes, and no clear driving factor between the FRI and FRII sources is found even when combining radio luminosity, accretion mode, large-scale environment and host galaxy luminosity.

The existence of a correlation between observed radio spectral index and redshift has long been used as a method for selecting high‐redshift radio galaxy candidates. We use nine highly spectroscopically complete radio samples, selected at different frequencies and flux limits, to determine the efficiency of this method and compare consistently observed correlations between spectral index (α), luminosity (P), linear size (D) and redshift (z) in our samples. We observe a weak correlation between z and α which remains even when Malmquist bias is removed. The strength of the z–α correlation is dependent on both the k‐correction and sample selection frequency, in addition to the frequency at which α is measured, and consistent results for both high‐ and low‐frequency‐selected samples are only seen if analysis is restricted to just extended radio galaxies. This fits with the popular interpretation that the spectra steepen with z because the radio lobes work against a denser intergalactic medium environment as z increases, out to z∼ 2–3. However, we also note that the majority of sources known at z > 4 are very compact and often display a negatively curved or peaked spectrum, indicative of youth or merger activity, and therefore the low‐frequency radio spectrum as a whole should be determined; this is something for which the new LOw Frequency ARray will be crucial. We quantify both the efficiency and the completeness of various techniques used to select high‐z radio candidates. A steep‐spectrum cut applied to low‐frequency‐selected samples can more than double the fraction of high‐z sources, but at a cost of excluding over half of the high‐z sources present in the original sample. An angular size cut is an almost as equally effective radio‐based method as a steep‐spectrum cut for maximizing the high‐z content of large radio samples, and works for both high‐ and low‐frequency‐selected samples. In multiwavelength data, selection first of infrared‐faint radio sources remains by far the most efficient method of selecting high‐z sources. We present a simple method for selecting high‐z radio sources, based purely on combining their observed radio properties of α and angular size, with the addition of the K‐band magnitude if available.

This paper focuses on a comparison of the space densities of Fanaroff-Riley type I (FR I) and FR II sources at different epochs, with a particular focus on FR I sources.First, we present the concluding steps in constructing the Combined NVSS-FIRST Galaxies (CoNFIG) catalogue, including new Very Large Array observations, optical identifications and redshift estimates. The final catalogue consists of 859 sources over four samples (CoNFIG-1, -2, -3 and -4 with flux density limits of S 1.4 GHz = 1.3, 0.8, 0.2 and 0.05 Jy, respectively). It is 95.7 per cent complete in radio morphology classification and 74.3 per cent of the sources have redshift data.Combining CoNFIG with complementary samples, the distribution and evolution of FR I and FR II sources are investigated. We find that FR I sources undergo mild evolution and that, at the same radio luminosity, FR I and FR II sources show similar space density enhancements in various redshift ranges, possibly implying a common evolution.

This paper presents the results of the 2009-2010 monitoring sessions of the starburst galaxy M82, obtained with the Multi-Element Radio-Linked Interferometer Network (MERLIN) at 5 GHz and e-MERLIN at 6 GHz. Combining several 5 GHz MERLIN epochs to form a map with 33.0 µJy/bm noise level, 52 discrete sources, mostly supernova remnants and Hii regions, are identified. These include three objects which were not detected in the 2002 5 GHz MERLIN monitoring session: supernova SN2008iz, the transient source 43.78+59.3, and a new supernova remnant shell. Flux density variations, in the long (1981 to 2010), medium (2002 to 2010) and short (2009 to 2010) term, are investigated. We find that flux densities of SNRs in M82 stay constant in most of the sample (∼95%). In addition, aside from SN2008iz and the well-known variable source 41.95+57.5, two sources display short and medium term variations over the period 2009-2010. These sources being among the most compact SNR in M82, these flux density variations could be due to changes in the circumstellar and interstellar medium in which the shocks travel.

The CoNFIG (Combined NVSS–FIRST Galaxies) sample is a new sample of 274 bright radio sources at 1.4 GHz. It was defined by selecting all sources with S1.4 GHz≥ 1.3 Jy from the NRAO Very Large Array (VLA) Sky Survey (NVSS) in the north field of the Faint Images of the Radio Sky at Twenty centimetres (FIRST) survey. New radio observations obtained with the VLA for 31 of the sources are presented. The sample has complete Fanaroff–Riley (FRI)/FRII morphology identification; optical identifications and redshifts are available for 80 and 89 per cent of the sample, respectively, yielding a mean redshift of ∼0.71. One of the goals of this survey is to get better definitions of luminosity distributions and source counts of FRI/FRII sources separately, in order to determine the evolution of the luminosity function for each type of source. We present a preliminary analysis, showing that these data are an important step towards examining various evolutionary schemes for these objects and to confirm or correct the dual population unified scheme for radio active galactic nuclei (AGN). Improving our understanding of radio galaxy evolution will give better insight into the role of AGN feedback in galaxy formation.