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Virtually all massive galaxies, including our own, host central black holes ranging in mass from millions to billions of solar masses. The growth of these black holes releases vast amounts of energy that powers quasars and other weaker active galactic nuclei. A tiny fraction of this energy, if absorbed by the host galaxy, could halt star formation by heating and ejecting ambient gas. A central question in galaxy evolution is the degree to which this process has caused the decline of star formation in large elliptical galaxies, which typically have little cold gas and few young stars, unlike spiral galaxies., Nature Review 7 pages, 5 figures

In the next few years, the Low Frequency Array (LOFAR) will open up one of the last astronomically unexplored wavelength regimes. While the LOFAR core is currently being erected in the Netherlands, its outer stations will cover a large part of Europe, resulting in an unprecedented angular resolution at > meter wavelengths. Next to many other exciting scientific endeavours, LOFAR will be the first instrument to probe the low frequency spectra of Gigahertz Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) radio sources. It will give new insights into their absorption processes, and probe associated extended emission (possibly linked to earlier epochs of activity) in these enigmatic class of young active galactic nuclei. Furthermore, LOFAR will be sensitive to possibly the most distant GPS and CSS sources, of which their spectral turnovers have redshifted down to the lowest observable radio frequencies. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

New results from a large survey of H-alpha emission-line galaxies at z=0.84 using WFCAM/UKIRT and a custom narrow-band filter in the J band are presented as part of the HiZELS survey. Reaching an effective flux limit of 1e-16 erg/s/cm^2 in a comoving volume of 1.8e5 Mpc^3, this represents the largest and deepest survey of its kind ever done at z~1. There are 1517 potential line emitters detected across 1.4 sq.deg of the COSMOS and UKIDSS UDS fields, of which 743 are selected as H-alpha emitters. These are used to calculate the H-alpha luminosity function, which is well-fitted by a Schechter function with phi*=10^(-1.92+-0.10) Mpc^-3, L*=10^(42.26+-0.05)erg/s, and alpha=-1.65+-0.15. The integrated star formation rate density (SFRD) at z=0.845 is 0.15+-0.01 M_sun/yr/Mpc^3. The results robustly confirm a strong evolution of SFRD from the present day out to z~1 and then flattening to z~2, using a single star-formation indicator. Out to z~1, both the characteristic luminosity and space density of the H-alpha emitters increase significantly; at higher redshifts, L* continues to increase, but phi* decreases. The z=0.84 H-alpha emitters are mostly disk galaxies (82+-3%), while 28+-4% of the sample show signs of merger activity and contribute ~20% to the total SFRD. Irregulars and mergers dominate the H-alpha luminosity function above L*, while disks are dominant at fainter luminosities. These results demonstrate that it is the evolution of 'normal' disk galaxies that drives the strong increase in the SFRD from the current epoch to z~1, although the continued strong evolution of L* beyond z=1 suggests an increasing importance of merger activity at higher redshifts., 17 pages, 13 figures. Accepted for publication in MNRAS

We describe multi-frequency data designed to probe the emission mechanism that dominates in faint radio sources. Our analysis is based on observations of the Lockman Hole using the GMRT - the deepest 610-MHz imaging yet reported - together with 1.4-GHz imaging from the VLA, well matched in resolution and sensitivity to the GMRT data. The GMRT and VLA data are cross-matched to obtain the radio spectral indices for the faint radio emitters. Statistical analyses show no clear evolution for the median spectral index, alpha, as a function of flux density. alpha is found to be -0.6 to -0.7, based on an almost unbiased 10-sigma criterion, down to a flux level of S(1.4GHz) >~ 100uJy. The fraction of inverted spectrum sources (alpha > 0) is less than 10%. The results suggest that the most prevalent emission mechanism in the sub-mJy regime is optically-thin synchrotron, ruling out a dominant flat spectrum or ultra-steep spectrum radio population. The spectral index distribution has a significant scatter, 0.4-0.5, which suggests a mixture of different populations at all flux levels. Spectroscopic classification of radio sources with X-ray emission has allowed us to estimate that the fraction of radio-quiet AGN at 30, Comment: In press at MNRAS, 18 pages

We investigate how the [OII] properties and the morphologies of galaxies in clusters and groups at z=0.4-0.8 depend on projected local galaxy density, and compare with the field at similar redshifts and clusters at low-z. In both nearby and distant clusters, higher-density regions contain proportionally fewer star-forming galaxies, and the average [OII] equivalent width of star-forming galaxies is independent of local density. However, in distant clusters the average current star formation rate (SFR) in star-forming galaxies seems to peak at densities ~15-40 galaxies Mpc^{-2}. At odds with low-z results, at high-z the relation between star-forming fraction and local density varies from high- to low-mass clusters. Overall, our results suggest that at high-z the current star formation (SF) activity in star-forming galaxies does not depend strongly on global or local environment, though the possible SFR peak seems at odds with this conclusion. We find that the cluster SFR normalized by cluster mass anticorrelates with mass and correlates with the star-forming fraction. These trends can be understood given a) that the average star-forming galaxy forms about 1 Msun/yr in all clusters; b) that the total number of galaxies scales with cluster mass and c) the dependence of star-forming fraction on cluster mass. We present the morphology-density (MD) relation for our z=0.4-0.8 clusters, and uncover that the decline of the spiral fraction with density is entirely driven by galaxies of types Sc or later. For galaxies of a given Hubble type, we see no evidence that SF properties depend on local environment. In contrast with recent findings at low-z, in our distant clusters the SF-density relation and the MD-relation are equivalent, suggesting that neither of the two is more fundamental than the other.(abr.), 21 pages, 14 figures, accepted for publication in ApJ

We have analysed the 24um properties of a radio-selected sample in the Subaru-XMM/Newton Deep Field in order to explore the behaviour of the FIR/radio relation at high redshifts. Statistically, the correlation is described by q24, the ratio between the observed flux densities at 24um and 1.4GHz, respectively. Using 24um data results in considerably more scatter in the correlation than previous work using data at 60-70um. Nevertheless, we do observe a steady correlation as a function of redshift, up to z~3.5, suggesting its validity back to primeval times. We find q24 = 0.30 +/- 0.56 for the observed and q24 = 0.71 +/- 0.47 for the k-corrected radio sample, based on sources with 300uJy < S(1.4GHz) < 3.2mJy and 24um detections. A suitable k-correction given by a M82-like mid-IR template suggests no extreme silicate absorption in the bulk of our radio sample. Using thresholds in q24 to identify radio-excess sources, we have been able to characterise the transition from radio-loud AGN to star-forming galaxies and radio-quiet AGN at faint (1mJy. The rest-frame U-B colours of the expected radio-excess population have redder distribution than those that follow the correlation. This is therefore a promising way to select obscured Type-2 AGN, with a radio loud nature, missed by deep X-ray observations. Spectroscopic follow-up of these sources is required to fully test this method., The paper contains 7 figures and 1 table. In press at MNRAS

We present a sample of clusters drawn from the C4 cluster catalog of the Sloan Digital Sky Survey, where particular emphasis has been placed on the correct identification of the Brightest Cluster Galaxy (BCG) and the determination of the velocity dispersion within the virial radius. In this sample, we investigate the occurence of radio-AGN activity in the BCGs. We find that the radio-loud fraction is enhanced by a factor of up to 10, compared to galaxies of the same mass that are not BCGs.

The Combined EIS-NVSS Survey Of Radio Sources (CENSORS) is a 1.4GHz radio survey selected from the NRAO VLA Sky Survey (NVSS) and complete to a flux-density of 7.2mJy. It targets the ESO Imaging Survey (EIS) Patch D, which is a 3 by 2 square degree field centred on 09 51 36.0, -21 00 00 (J2000). This paper presents the results of spectroscopic observations of 143 of the 150 CENSORS sources. The primary motivation for these observations is to achieve sufficient spectroscopic completeness so that the sample may be used to investigate the evolution of radio sources. The observations result in secure spectroscopic redshifts for 63% of the sample and likely redshifts (based on a single emission line, for example) for a further 8%. Following the identification of the quasars and star-forming galaxies in the CENSORS sample, estimated redshifts are calculated for the remainder of the sample via the K-z relation for radio galaxies. Comparison of the redshift distribution of the CENSORS radio sources to distributions predicted by the various radio luminosity function evolution models of Dunlop & Peacock 1990, results in no good match. This demonstrates that this sample can be used to expand upon previous work in that field., Accepted for publication in MNRAS. This version has some reduced resolution figures and 13 associated gif files. A version with all figures incorporated (at full resolution) is available at http://www.roe.ac.uk/~pnb/papers/censors_spectro.pdf

We present results from a near-infrared narrow-band survey of emission-line galaxies at z=2.23, using the Wide Field Camera on the United Kingdom Infrared Telescope. The H2S1 narrow-band filter (lambda_c=2.121um) we employ selects the H-alpha emission line redshifted to z=2.23, and is thus suitable for selecting 'typical' star forming galaxies and active galactic nuclei at this epoch. The pilot study was undertaken in the well studied Cosmological Evolution Survey field (COSMOS) and is already the largest near-infrared narrow-band survey at this depth, with a line flux limit of F(H-alpha)~10^-16 erg/s/cm^2 over 0.60 square degrees, probing ~220x10^3 Mpc^3 (co-moving) down to a limiting star formation rate of 30 M_sun/yr (3sigma). In this paper we present the results from our pilot survey and evaluate the H-alpha luminosity function and estimate the clustering properties of H-alpha emitters at z=2.23 from 55 detected galaxies. The integrated luminosity function is used to estimate the volume averaged star formation rate at z=2.23: SFRD = 0.17^{+0.16}_{-0.09} M_sun/yr/Mpc^3 for L(H-alpha) > 10^42 erg/s. For the first time, we use the H-alpha star-formation tracer to reliably constrain SFRD out to z=2.23 demonstrating the rapid increase in SRFD out to this redshift as well as confirming the flattening in SFRD between z~1-2. In addition to the luminosity distribution, we analyse the clustering properties of these galaxies. Using the 2-point angular correlation function, we estimate a real space correlation length of r_0= 4.2^{+0.4}_{-0.2} h^-1 Mpc. In comparison to models of clustering which take into account bias evolution, we estimate that these galaxies are hosted by dark matter halos of mass M_halo ~ 10^12 M_sun consistent with the progenitors of the Milky Way., 15 pages, 10 figures. Accepted for publication in MNRAS. High-resolution version available at http://astro.dur.ac.uk/~jgeach/HiZELS_COSMOS_H2S1.pdf

This erratum corrects a number of formulae containing mistakes in the paper 'Luminosity function, sizes and FR dichotomy of radio-loud AGN', 2007, MNRAS, v. 381, p.1548. The corrections do not alter any of the conclusions in the original paper., single page, no figures, erratum to MNRAS, 2007, v. 381, p. 1548

We present XMM data for the supercluster A901/2, at z ~ 0.17, which is combined with deep imaging and 17-band photometric redshifts (from the COMBO-17 survey), 2dF spectra and Spitzer 24um data, to identify AGN in the supercluster. The 90ksec XMM image contains 139 point sources, of which 11 are identified as supercluster AGN with L_X(0.5-7.5keV) > 1.7x10^41 erg/cm2/s. The host galaxies have M_R 98 per cent significance. The AGN host galaxies lie predominantly in areas of moderate projected galaxy density and with more local blue galaxies than the control sample, with the exception of one very bright Type I AGN very near the centre of a cluster. These environments are similar to, but not limited to, cluster outskirts and blue groups. Despite the large number of potential host galaxies, no AGN are found in regions with the highest galaxy density (excluding some cluster cores where emission from the ICM obscures moderate luminosity AGN). AGN are also absent from the areas with lowest galaxy density. We conclude that the prevalence of cluster AGN is linked to their environment.

The radio luminosity function (RLF) of radio galaxies and radio-loud quasars is often modelled as a broken power-law. The break luminosity is close to the dividing line between the two Fanaroff-Riley (FR) morphological classes for the large-scale radio structure of these objects. We use an analytical model for the luminosity and size evolution of FRII-type objects together with a simple prescription for FRI-type sources to construct the RLF. We postulate that all sources start out with an FRII-type morphology. Weaker jets subsequently disrupt within the quasi-constant density cores of their host galaxies and develop turbulent lobes of type FRI. With this model we recover the slopes of the power laws and the break luminosity of the RLF determined from observations. The rate at which AGN with jets of jet power $Q$ appear in the universe is found to be proportional to $Q^{-1.6}$. The model also roughly predicts the distribution of the radio lobe sizes for FRII-type objects, if the radio luminosity of the turbulent jets drops significantly at the point of disruption. We show that our model is consistent with recent ideas of two distinct accretion modes in jet-producing AGN, if radiative efficiency of the accretion process is correlated with jet power., 13 pages, 1 figure, accepted by MNRAS

We use the Sloan Digital Sky Survey to construct a sample of 625 brightest group and cluster galaxies (BCGs) together with control samples of non-BCGs matched in stellar mass, redshift, and color. We investigate how the systematic properties of BCGs depend on stellar mass and on their privileged location near the cluster center. The groups and clusters that we study are drawn from the C4 catalogue of Miller et al. (2005) but we have developed improved algorithms for identifying the BCG and for measuring the cluster velocity dispersion. Since the SDSS photometric pipeline tends to underestimate the luminosities of large galaxies in dense environments, we have developed a correction for this effect which can be readily applied to the published catalog data. We find that BCGs are larger and have higher velocity dispersions than non-BCGs of the same stellar mass, which implies that BCGs contain a larger fraction of dark matter. In contrast to non-BCGs, the dynamical mass-to-light ratio of BCGs does not vary as a function of galaxy luminosity. Hence BCGs lie on a different fundamental plane than ordinary elliptical galaxies. BCGs also follow a steeper Faber-Jackson relation than non-BCGs, as suggested by models in which BCGs assemble via dissipationless mergers along preferentially radial orbits. We find tentative evidence that this steepening is stronger in more massive clusters. BCGs have similar mean stellar ages and metallicities to non-BCGs of the same mass, but they have somewhat higher alpha/Fe ratios, indicating that star formation may have occurred over a shorter timescale in the BCGs. Finally, we find that BCGs are more likely to host radio-loud active galactic nuclei than other galaxies of the same mass, but are less likely to host an optical AGN. The differences we find are more pronounced for the less massive BCGs., Comment: Replaced with slightly modified version accepted by MNRAS. 28 pages, 25 figures. Version with full resolution figures available at http://www.mpa-garching.mpg.de/~anja/bcgs_avdl.pdf

The role of radio-loud active galactic nuclei (AGN) in continually re-heating the cooling gas in the haloes surrounding elliptical galaxies, and in clusters of galaxies, is investigated. The prevalence of radio-loud AGN activity amongst elliptical galaxies is found to scale strongly with the mass of the central black hole (as M1.6 BH). Combining this result with estimates of the mechanical energy output of these radio sources, the time-averaged energy output associated with recurrent radio source activity is derived: for elliptical galaxies of all masses, this is shown to balance the radiative energy losses from the hot gas surrounding the galaxy. Recurrent radio-loud AGN activity may therefore provide a self-regulating feedback mechanism capable of controlling the rate of growth of galaxies. The prevalence of radio-loud AGN activity amongst brightest cluster galaxies, and other cluster members is also determined, to investigate AGN feedback in galaxy clusters. Unless the efficiency of converting AGN mechanical energy into heating increases by 2–3 orders of magnitude between groups and rich clusters, radio–mode heating will not balance radiative cooling in systems of all masses.

With the goal of identifying high redshift radio galaxies with FRI classification, here are presented high resolution, wide-field radio observations, near infra-red and optical imaging and multi-object spectroscopy of two fields of the Leiden-Berkeley Deep Survey. These fields, Hercules.1 and Lynx.2, contain a complete sample of 81 radio sources with S(1.4 GHz) > 0.5 mJy within 0.6 square degrees. This sample will form the basis for a study of the population and cosmic evolution of high redshift, low power, FRI radio sources which will be presented in Paper II. Currently, the host galaxy identification fraction is 86% with 11 sources remaining unidentified at a level of r > 25.2 mag (Hercules; 4 sources) or r > 24.4 mag (Lynx; 7 sources) or K > 20 mag. Spectroscopic redshifts have been determined for 49% of the sample and photometric redshift estimates are presented for the remainder of the sample., Accepted by MNRAS; 24 pages, 7 figures. A full version, including figures is available at http://www.roe.ac.uk/~eer/eer_paper.ps

During the course of this conference, much evidence was presented that points to an intimate connection between the energetic outflows driven by AGN and the energy budget and quite possibly also the evolution of their gaseous environments. However, it is still not clear if and how the AGN activity is triggered by the cooling gas, how long the activity lasts for and how these effects give rise to the observed distribution of morphologies of the outflows. In this contribution we concentrate on the high radio luminosity end of the AGN population. While most of the heating of the environmental gas may be due to less luminous and energetic outflows, these more powerful objects have a very profound influence on their surroundings. We will describe a simple model for powerful radio galaxies and radio-loud quasars that explains the dichotomy of their large-scale radio morphologies as well as their radio luminosity function.

We present XMM–Newton observations of three optically selected z > 0.6 clusters from the European Southern Observatory (ESO) Distant Cluster Survey (EDisCS), comprising the first results of a planned X-ray survey of the full EDisCS high-redshift sample. The EDisCS clusters were identified in the Las Campanas Distant Cluster Survey as surface brightness fluctuations in the optical sky and their masses and galaxy populations are well described by extensive photometric and spectroscopic observations. We detect two of the three clusters in the X-ray and place a firm upper limit on diffuse emission in the third cluster field. We are able to constrain the X-ray luminosity and temperature of the detected clusters and estimate their masses. We find that the X-ray properties of the detected EDisCS clusters are similar to those of X-ray-selected clusters of comparable mass and – unlike other high-redshift, optically selected clusters – are consistent with the T–σ and LX–σ relations determined from X-ray-selected clusters at low redshift. The X-ray determined mass estimates are generally consistent with those derived from weak-lensing and spectroscopic analyses. These preliminary results suggest that the novel method of optical selection used to construct the EDisCS catalogue may, like selection by X-ray luminosity, be well suited for identification of relaxed, high-redshift clusters whose intracluster medium is in place and stable by z ∼ 0.8., The related data "X-ray properties of 3 EDisCS galaxy clusters (Johnson+, 2006)" is available in the VizieR Catalogue at http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=J%2FMNRAS%2F371%2F1777

There are three major axes to describe the evolution of galaxies, namely, time (redshift), space (environment) and mass (stellar mass). In this article, one topic each will be presented along these axes. (1) Based on the Subaru wide-field (30') optical imaging of two distant clusters (z=0.55 and 0.83), we show the large scale structures in galaxy distributions on a scale greater than 10Mpc, which serve as an evidence for hierarchical growth of rich clusters of galaxies through assembly of surrounding groups. (2) Based on the deep NIR imaging of high-z clusters at z~1 and 1.5, we show massive galaxies in clusters have assembled most of their mass by z=1.5, which is earlier than the hierarchical model predictions. (3) Based on the Subaru deep and wide optical imaging of Subaru/XMM-Newton Deep Survey Field, we show a deficit of red and faint galaxies and a lack of blue massive galaxies in the high density regions at z~1, which suggest down-sizing in galaxy formation as apparently opposed to the CDM-based bottom-up scenario.

The XMM Large Scale Structure survey (XMM-LSS) is an X-ray survey aimed at studying the large scale structure of the Universe. The XMM-LSS field is currently being followed up using observations across a wide range of wavelengths, and in this paper we present the observational results of a low frequency radio survey of the XMM-LSS field using the Very Large Array at 74 and 325 MHz. This survey will map out the locations of the extragalactic radio sources relative to the large scale structure as traced by the X-ray emission. This is of particular interest because radio galaxies and radio loud AGN show strong and complex interactions with their small and larger scale environment, and different classes of radio galaxies are suggested to lie at different places with respect to the large scale structure. For the phase calibration of the radio data, we used standard self-calibration at 325 MHz and field-base calibration at 74 MHz. Polyhedron-based imaging as well as mosaicing methods were used at both frequencies. At 74 MHz we have a resolution of $30''$, a median $5\sigma$ sensitivity of $\sim162$ mJy/beam and we detect 666 sources over an area of 132 square degrees. At 325 MHz, we have a resolution of $6.7''$, a median $5\sigma$ sensitivity of 4 mJy/beam, and we detect 847 sources over an area of 15.3 square degrees. At 325 MHz we have detected a region of diffuse radio emission which is a cluster halo or relic candidate.

We study how the proportion of star-forming galaxies evolves between z=0.8 and z=0 as a function of galaxy environment, using the [OII] line in emission as a signature of ongoing star formation. Our high-z dataset comprises 16 clusters, 10 groups and another 250 galaxies in poorer groups and the field at z=0.4-0.8 from the ESO Distant Cluster Survey, plus another 9 massive clusters at similar redshifts. As a local comparison, we use samples of galaxy systems selected from the Sloan Digital Sky Survey at 0.04< z < 0.08. At high-z most systems follow a broad anticorrelation between the fraction of star-forming galaxies and the system velocity dispersion. At face value, this suggests that at z=0.4-0.8 the mass of the system largely determines the proportion of galaxies with ongoing star formation. At these redshifts the strength of star formation (as measured by the [OII] equivalent width) in star-forming galaxies is also found to vary systematically with environment. Sloan clusters have much lower fractions of star-forming galaxies than clusters at z=0.4-0.8 and, in contrast with the distant clusters, show a plateau for velocity dispersions $ \ge 550 km s^-1$, where the fraction of galaxies with [OII] emission does not vary systematically with velocity dispersion. We quantify the evolution of the proportion of star-forming galaxies as a function of the system velocity dispersion and find it is strongest in intermediate-mass systems (sigma ~ 500-600 km s^-1 at z=0). To understand the origin of the observed trends, we use the Press-Schechter formalism and the Millennium Simulation and show that galaxy star formation histories may be closely related to the growth history of clusters and groups. We propose a scheme that is able to account for the observed relations between the star-forming fraction and ��[abridged]., 28 pages, 19 figures, ApJ in press

(abridged) Powerful radio galaxies often display enhanced optical/UV emission regions, elongated and aligned with the radio jet axis. The aim of this series of papers is to separately investigate the effects of radio power and redshift on the alignment effect, together with other radio galaxy properties. In this second paper, we present a deeper analysis of the morphological properties of these systems, including both the host galaxies and their surrounding aligned emission. The host galaxies of our 6C subsample are well described as de Vaucouleurs ellipticals, with typical scale sizes of ~10kpc. This is comparable to the host galaxies of low-z radio sources of similar powers, and also the more powerful 3CR sources at the same redshift. The contribution of nuclear point source emission is also comparable, regardless of radio power. The 6C alignment effect is remarkably similar to that seen around more powerful 3CR sources at the same redshift in terms of extent and degree of alignment with the radio source axis, although it is generally less luminous. The bright, knotty features observed in the case of the z~1 3CR sources are far less frequent in our 6C subsample; neither do we observe such strong evidence for evolution in the strength of the alignment effect with radio source size/age. However, we do find a very strong link between the most extreme alignment effects and emission line region properties indicative of shocks, regardless of source size/age or power. In general, the 6C alignment effect is still considerably stronger than that seen around lower redshift galaxies of similar radio powers. (abridged), 23 pages, 15 figures, accepted for publication in MNRAS. See http://www.mrao.cam.ac.uk/~kji/MorphPaper/ for version of paper with full resolution images of Figs 1-10

We present the ESO Distant Cluster Survey (EDisCS) a survey of 20 fields containing distant galaxy clusters with redshifts ranging from 0.4 to almost 1.0. Candidate clusters were chosen from among the brightest objects identified in the Las Campanas Distant Cluster Survey, half with estimated redshift z_est~0.5 and half with z_est~0.8. They were confirmed by identifying red sequences in moderately deep two colour data from VLT/FORS2. For confirmed candidates we have assembled deep three-band optical photometry using VLT/FORS2, deep near-infrared photometry in one or two bands using NTT/SOFI, deep optical spectroscopy using VLT/FORS2, wide field imaging in two or three bands using the ESO Wide Field Imager, and HST/ACS mosaic images for 10 of the most distant clusters. This first paper presents our sample and the VLT photometry we have obtained. We present images, colour-magnitude diagrams and richness estimates for our clusters, as well as giving redshifts and positions for the brightest cluster members. Subsequent papers will present our infrared photometry, spectroscopy, HST and wide-field imaging, as well as a wealth of further analysis and science results. Our reduced data become publicly available as these papers are accepted., 21 pages, 6 figures, A&A in press. A version with full resolution figures is available at http://www.mpa-garching.mpg.de/ediscs/papers.html

By combining the 2-degree Field Galaxy Redshift Survey with the NRAO VLA Sky Survey at 1.4 GHz, the environments of radio loud AGN in the nearby Universe are investigated using both local projected galaxy densities and a friends-of-friends group finding algorithm. Radio-loud AGN are preferentially located in galaxy groups and poor-to-moderate richness galaxy clusters. The AGN fraction appears to depend more strongly on the large-scale environment (group, cluster, etc) in which a galaxy is located than on its more local environment, except at the lowest galaxy surface densities where practically no radio-loud AGN are found. The ratio of absorption-line to emission-line AGN changes dramatically with environment, with essentially all radio-loud AGN in rich environments showing no emission lines. This result could be connected with the lack of cool gas in cluster galaxies, and may have important consequences for analyses of optically-selected AGN, which are invariably selected on emission line properties. The local galaxy surface density of the absorption-line AGN is strongly correlated with radio luminosity, implying that the radio luminosities may be significantly boosted in dense environments due to confinement by the hot intracluster gas. The environments of a radio-selected sample of star forming galaxies are also investigated to provide an independent test of optical studies. In line with those studies, the fraction of star forming galaxies is found to decrease strongly with increasing local galaxy surface density; this correlation extends across the whole range of galaxy surface densities, with no evidence for the density threshold found in some optical studies., Comment: Accepted for publication in MNRAS. LaTeX, 13 pages

(Abridged) Deep VLT spectropolarimetric observations are presented for two powerful radio galaxies, 0850-206 and 1303+091. These observations cover the rest-frame wavelength range ~ 1450 - 3750 A. New radio observations and continuum images of the same sources are also presented. These galaxies are the first two observed from a complete sample of nine radio sources with redshifts in the range 1.3 < z < 1.5 (selected from the equatorial sample of powerful radio sources of Best, Rottgering & Lehnert), as part of a project aimed to investigate the multi-component nature of the UV continuum in radio galaxies and any variations of the continuum properties with the radio source age. The larger radio source of the two, 0850-206, presents a high continuum fractional polarization, averaging 17% across the observed wavelength range and reaching 24% at rest-frame wavelengths of 3000 A. For both galaxies, the position angle of the electric vector is generally constant with wavelength and within ~15 degrees of perpendicular to the radio axis. Both their total flux spectra and polarized flux spectra reveal the 2200 A dust feature, and comparison with dust scattering models suggests that the composition of the dust in these galaxies is similar to that of Galactic dust. In 0850-206, scattered quasar radiation dominates the UV continuum emission, with the nebular continuum accounting for no more than ~22% and no requirement for any additional emission component such as emission from young stars. By contrast, in 1303+091, unpolarized radiation could be a major constituent of the UV continuum emission, with starlight accounting for up to ~50% and the nebular continuum accounting for ~11%., 20 pages, including 14 figures. MNRAS accepted

We are undertaking the first systematic study of the prevalence of AGN activity in a large sample of high redshift galaxy clusters. Local clusters contain mainly red elliptical galaxies, and have little or no luminous AGN activity. However, recent studies of some moderate to high redshift clusters have revealed significant numbers of luminous AGN within the cluster. This effect may parallel the Butcher-Oemler effect - the increase in the fraction of blue galaxies in distant clusters compared to local clusters. Our aim is to verify and quantify recent evidence that AGN activity in dense environments increases with redshift, and to evaluate the significance of this effect. As cluster AGN are far less prevalent than field sources, a large sample of over 120 cluster fields at z > 0.1 has been selected from the Chandra archives and is being analysed for excess point sources. The size of the excess, the radial distribution and flux of the sources and the dependence of these on cluster redshift and luminosity will reveal important information about the triggering and fueling of AGN., 2 pages, to appear in proceedings of 'Multi-wavelength AGN surveys', Cozumel, 2003

Best, Rottgering and Lehnert (1999, 2000a) defined a new sample of powerful radio sources from the Molonglo Reference Catalogue, for which redshifts were compiled or measured for 177 of the 178 objects. For the final object, MRC1059-010 (3C249), the host galaxy is here identified using near-infrared imaging, and the redshift is determined from VLT spectroscopy. For one other object in the sample, MRC0320+053 (4C05.14), the literature redshift has been questioned: new spectroscopic observations of this object are presented, deriving a corrected redshift. With these two results, the spectroscopic completeness of this sample is now 100%. New redshifts are also presented for PKS0742+10 from the Wall & Peacock 2.7 GHz catalogue, and PKS1336+003 from the Parkes Selected Regions. PKS0742+10 shows a strong neutral hydrogen absorption feature in its Lyman-alpha emission profile., 4 pages. LaTeX. Accepted for publication in MNRAS

The results of Hubble Space Telescope and UKIRT imaging observations are presented for a sample of 11 6C radio galaxies with redshifts 0.85 < z < 1.5. The observations of the 6C sources reveal a variety of different features, similar to those observed around the higher luminosity of the aligned emission appears less extreme in the case of the 6C radio galaxies. For both samples, the aligned emission clearly cannot be explained by a single emission mechanism; line emission and related nebular continuum emission, however, often provide a significant contribution to the aligned emission., 17 pages, 11 figures (figs 3,6,11 low resolution - full resolution images can be obtained from http://www.mrao.cam.ac.uk/~kji/ImagingFigs/). Accepted for publication in MNRAS

Powerful radio galaxies often display enhanced optical/UV continuum emission and extended emission line regions, elongated and aligned with the radio jet axis. The expansion of the radio source strongly affects the gas clouds in the surrounding IGM, and the kinematic and ionization properties of the extended emission line regions display considerable variation over the lifetime of individual sources, as well as with cosmic epoch. We present the results of deep rest-frame UV and optical imaging and UV spectroscopy of high redshift 6C radio galaxies. The interdependence of the host galaxy and radio source properties are discussed, considering: (i) the relative contribution of shocks associated with the expanding radio source to the observed emission line gas kinematics, and their effect on the ionization state of the gas; (ii) the similarities and differences between the morphologies of the host galaxies and aligned emission for a range of radio source powers; and (iii) the influence of radio power on the strength of the observed alignment effect., LaTeX, 6 pages, 5 figures, Elsevier Science format. To appear in "Radio galaxies: past, present & future". eds. M. Jarvis et al., Leiden, Nov 2002

The environments of a complete subsample of 6 of the most powerful radio-loud AGN at redshifts z~1.6 are investigated, using deep RJK imaging to depths of R~26, J~22.4 and K~20.6. An excess of galaxy counts in the K-band is seen across these fields; these are predominantly associated with red galaxies (R-K>4) of magnitudes 17.54) galaxies, suggesting that the morphology-density relation is imprinted into the centres of clusters at a high redshift. (ii) weaker large-scale excesses extending out to between 1 and 1.5 Mpc radius. The presence or absence of galaxy excesses on these two scales, however, differs greatly between the six different fields. The implications of these results for both cluster formation and the nature of high redshift AGN are discussed (abridged)., Comment: Accepted for publication in MNRAS. LaTeX, 16 pages, plus 12 additional jpeg figures, 6 in colour. A version with all figures in the postscript file is available from http://www.roe.ac.uk/~pnb/eso_clus.ps

We define 3 samples of extragalactic radio sources of type FRII, containing 26 objects in total. The control sample consists of 6C and 7C sources with radio powers of around 10e27 W\Hz at 151 MHz and redshifts of around z=1. The other samples contain 3CRR sources with either comparable redshifts but radio powers about a decade larger or with comparable radio powers but redshifts around z = 0.4. We use these samples to investigate the possible evolution of their depolarisation and rotation measure properties with redshift and radio power independently. We used VLA data for all sources at 4800 MHz and two frequencies within the 1400 MHz band, either from our own observations or from the archive. We present maps of the total intensity flux, polarised flux, depolarisation, spectral index, rotation measure and magnetic field direction where not previously published. Radio cores were detected in twelve of the twenty-six radio sources. Fourteen of the sources show a strong Laing-Garrington effect but almost all of the sources show some depolarisation asymmetry. All sources show evidence for an external Faraday screen being responsible for the observed depolarisation. We find that sources at higher redshift are more strongly depolarised. Rotation measure shows no trend with either redshift or radio power, however variations in the rotation measure across individual sources increase with the redshift of the sources but do not depend on their radio power., Comment: 21 pages, very low resolution version 33 figures. Accepted to MNRAS. High resolution paper at http://www.astro.soton.ac.uk/~jag/paper.html

A new sample of radio sources, with the designated name CENSORS (A Combined EIS-NVSS Survey Of Radio Sources), has been defined by combining the NRAO VLA Sky Survey (NVSS) at 1.4 GHz with the ESO Imaging Survey (EIS) Patch D, a 3 by 2 degree region of sky centred at 09 51 36.0, -21 00 00 (J2000). New radio observations of 199 NVSS radio sources with NVSS flux densities S(1.4GHz) > 7.8mJy are presented, and compared with the EIS I-band imaging observations which reach a depth of I~23; optical identifications are obtained for over two-thirds of the ~150 confirmed radio sources within the EIS field. The radio sources have a median linear size of 6 arcseconds, consistent with the trend for lower flux density radio sources to be less extended. Other radio source properties, such as the lobe flux density ratios, are consistent with those of brighter radio source samples. From the optical information, 30-40% of the sources are expected to lie at redshifts z >~ 1.5. One of the key goals of this survey is to accurately determine the high redshift evolution of the radio luminosity function. These radio sources are at the ideal flux density level to achieve this goal; at redshifts z~2 they have luminosities which are around the break of the luminosity function and so provide a much more accurate census of the radio source population at those redshifts than the existing studies of extreme, high radio power sources. Other survey goals include investigating the dual--population unification schemes for radio sources, studying the radio luminosity dependence of the evolution of radio source environments, and understanding the radio power dependence of the K-z relation for radio galaxies., Accepted for publication in MNRAS. 28 pages plus 36 reduced resolution jpeg figures. A postscript version with full resolution figures included in the text is available from http://www.roe.ac.uk/~pnb/censors.ps.gz

The importance of studying old elliptical galaxies at redshift z ~ 1.5 is reviewed, considering both what can be learned by extending studies of the evolution of cluster galaxy scaling relations to earlier cosmic epochs, and the age-dating of old elliptical galaxies at high redshifts. Following this, the first results are provided of an on-going project to find such distant elliptical galaxies, through an investigation of the cluster environments of powerful radio sources with redshifts 1.44 < z < 1.7. These studies show a considerable excess of red galaxies in the radio sources fields, with the magnitudes (K >~ 17.5) and colours (R-K > 4) expected of old passively evolving galaxies at the radio source redshift. The red galaxy overdensities are found on two different scales around the radio sources; a pronounced small-scale peak at radial distances of, Comment: LaTeX, 6 pages, Elsevier Science format. To appear in "Radio galaxies: past, present & future". eds. M. Jarvis et al., Leiden, Nov 2002

The presence of two distant FR I radio galaxies in the Hubble Deep Field plus Flanking Fields indicates that the number density of these objects is about 10-50 times higher at z>1 than in the local universe. This is in strong contrast with the idea that FR Is undergo no cosmological evolution. We advocate that the cosmological evolution of radio sources may be independent of FR class, and instead solely a function of radio power. In this scenario the evolutionary properties of extragalactic radio sources can be fully described within a `single population scheme'., LaTeX, 6 pages, 1 fig: Elsevier science format - NAR. Proceedings of the workshop "Radio galaxies: past, present & future". eds. Matt Jarvis et al. Leiden, Nov, 2002

The results of a spectroscopic analysis of 3CR and 6C radio galaxies at redshift z~1 are contrasted with the properties of lower redshift radio galaxies, chosen to be matched in radio luminosity to the 6C sources studied at z~1, thus enabling the P-z degeneracy to be broken. Partial rank correlations and principal component analysis have been used to determine which of z and P are the critical parameters underlying the observed variation of the ionization state andd kinematics of the emission line gas. [OII]/H-beta is shown to be a useful ionization mechanism diagnostic. Statistical analysis of the data shows that the ionization state of the emission line gas is strongly correlated with radio power, once the effects of other parameters are removed. No dependence of ionization state on z is observed, implying that the ionization state of the emission line gas is solely a function of the AGN properties rather than the hostt galaxy and/or environment. Statistical analysis of the kinematic properties of the emission line gas shows that these are strongly correlated independently withh both P and z. The correlation with redshift is the stronger of the two, suggesting that host galaxy composition or environment may play a role in producing the less extreme gas kinematics observed in the emission line regions of low redshift galaxies. For both the ionization and kinematic properties of thee galaxies, the independent correlations observed with radio size are strongest. Radio source age is a determining factor for the extended emission line regions., 10 pages, 5 figures, accepted for publication in MNRAS

(abridged) The results of deep long-slit optical spectroscopy for a sample of 8 6C radio galaxies at z~1 are presented. Emission line ratios are derived for emission lines with rest-frame wavelengths of 1500 - 4500Ang, and the kinematic propertiess of the emission line gas are derived from an analysis of the 2-d structure of thee [OII]3727 Ang emission line at ~5Ang spectral resolution. In general, the 6C spectra display many characteristics similar to those of more powerful 3CR sources at the same redshifts. The emission line region gas kinematics are more extreme for the smaller radio sources in the sample, which often display distorted velocity profiles. The ionization state of the emission line region also varies with radio size: the spectra of large radio sources (>120kpc) are consistent with photoionization by an obscured AGN, whilst smaller (, 29 pages, 22 figures, accepted for publication in MNRAS

Deep sub-millimetre observations using SCUBA are presented of the central regions of four high redshift clusters which have been extensively studied optically: CL0023+0423 (z=0.84), J0848+4453 (z=1.27), CL1604+4304 (z=0.90) and CL1604+4321 (z=0.92). 10 sub-millimetre sources are securely detected towards these four clusters at 850 microns, with two further tenuous detections; the raw 850 micron source counts exceed those determined from blank-field surveys by a factor of 3-4. In particular, towards CL1604+4304, 6 sources are detected with S(850) > 4 mJy making this the richest sub-mm field discovered to date. Corrections for gravitational lensing by these high redshift clusters reduce these excess sources counts, but are unlikely to account for more than about half of the excess, with the remainder presumably directly associated with cluster galaxies. The 450 to 850 micron flux density ratios of the detected sources are systematically higher (at a significance level > 98%) than those determined for blank-field selected sources, consistent with them being at the cluster redshifts. If subsequent identifications confirm cluster membership, these results will demonstrate that the optical Butcher-Oemler effect is also observed at sub-mm wavelengths., MNRAS, in consideration. 11 pages, including 6 figures. Minor typos corrected

Carbon radio recombination lines (RRLs) at low frequencies (, Comment: 6 pages, 5 figures, accepted for publication in ApJL

An extremely deep 5 GHz radio observation is presented of the rich cluster MS1054-03 at redshift z=0.83. 34 radio sources are detected down to a 32 micro-Jy (6 sigma), compared to about 25 expected from previous blank field radio source count determinations; the sources giving rise to these excess counts lie within 2 arcmins (700 kpc) of the cluster centre. Existing imaging and spectroscopy has provided optical identifications for 21 of the radio sources and redshifts for 11, of which 8 are confirmed cluster members. 4 of these 8 confirmed cluster sources are associated with close galaxy pairs (10-25 kpc projected offset) of similar magnitude, implying that the radio source may be triggered by an interaction. However, although MS1054-03 has a very high fraction (17%) of on-going mergers (separations 75%) is higher than at these flux density levels in the field (40-50%)., Comment: 19 pages LaTeX, including 8 figures. Accepted for publication in MNRAS. Version with higher resolution figures available from http://www.roe.ac.uk/~pnb/papers.html

Deep long-slit spectroscopic data are presented for a sample of 14 3CR radio galaxies at redshift z ~ 1, previously studied in detail using the Hubble Space Telescope, the Very Large Array, and UKIRT. Analysis of the [OII] 3727 emission line structures at 5 Ang spectral resolution is carried out to derive the kinematic properties of the emission line gas. In line with previous, lower resolution, studies, a wide variety of kinematics are seen, from gas consistent with a mean rotational motion through to complex structures with velocity dispersions exceeding 1000 kms. The data confirm the presence of a high velocity gas component in 3C265 and detached emission line systems in 3C356 and 3C441, and show for the first time that the emission line gas in the central regions of 3C324 is composed of two kinematically distinct components. Emission line fluxes and the colour of the continuum emission are determined down to unprecedently low observed wavelengths, lambda < 3500 Ang, sufficiently short that any contribution of an evolved stellar population is negligible. An accompanying paper investigates the variation in the emission line ratios and velocity structures within the sample, and draws conclusions as to the origin of the ionisation and kinematics of these galaxies., 23 pages LaTeX, including 16 figures. Accepted for publication in MNRAS

An analysis of the kinematics and ionisation state of the emission line gas of a sample of 14 3CR radio galaxies with redshifts z~1 is carried out. The data used for these studies, deep long--slit spectroscopic exposures from the WHT, are presented in an accompanying paper. It is found that radio sources with small linear sizes (, 15 pages LaTeX, including 10 figures. Accepted for publication in MNRAS

A new sample of very powerful radio galaxies is defined from the Molonglo Reference Catalogue, according to the criteria S (408 MHz) > 5 Jy, -30 < Dec < 10 degrees, |b| > 10 degrees. The sample is selected to have similar properties to the northern 3CR revised sample, and to be visible to a combination of existing northern telescopes such as the Very Large Array radio interferometer and large southern hemisphere telescope facilities. The sample contains 178 sources, of which spectroscopic redshifts are available in the literature for 128. For the remaining 50 sources, new radio imaging, optical imaging and spectroscopic observations are presented to identify the host galaxies and determine their redshifts. With these new observations the total sample is 100% optically identified and redshifts are available for 174 (98%) of the sources. The sample consists of one starburst galaxy, one Seyfert galaxy, 127 radio galaxies and 49 quasars. Basic properties of the sample, such as the distributions of the quasar and radio galaxy populations in redshift and their locations on the radio power versus linear size (P-D) diagram, show no significant differences from the revised 3CR sample. The equatorial location and the high spectroscopic completeness of this sample make it a valuable resource for detailed studies of the nature and environments of these important objects with the new generation of southern hemisphere telescopes., LaTeX. MNRAS in press. Revised to include more radio and spectroscopic data for the sample. Also includes new figures and an expanded discussion of sample properties. Figures 2-50 not supplied here; a version including these figures 2-50 is available at http://www.strw.leidenuniv.nl/~pbest/equatpap.ps An electronic version of the sample data table is available at http://www.strw.leidenuniv.nl/~pbest/equatpap.dat