Radio Sources in the 2dF Galaxy Redshift Survey. I. Radio Source Populations

We present the first results from a study of the radio continuum properties of galaxies in the 2dF Galaxy Redshift Survey, based on thirty 2dF fields covering a total area of about 100 square degrees. About 1.5% of galaxies with b(J) < 19.4 mag are detected as radio continuum sources in the NRAO VLA Sky Survey (NVSS). Of these, roughly 40% are star-forming galaxies and 60% are active galaxies (mostly low-power radio galaxies and a few Seyferts). The combination of 2dFGRS and NVSS will eventually yield a homogeneous set of around 4000 radio-galaxy spectra, which will be a powerful tool for studying the distriibution and evolution of both AGN and starburst galaxies out to redshift z=0.3.Comment: 14 pages, 7 figures, accepted for publication in PAS

Constraining the evolution of young radio-loud AGN

GPS and CSS radio sources are the objects of choice to investigate the evolution of young radio-loud AGN. Previous investigations, mainly based on number counts and source size distributions, indicate that GPS/CSS sources decrease significantly in radio power when evolving into old, extended objects. We suggest this is preceded by a period of increase in radio luminosity, which lasts as long as the radio source is confined within the core-radius of its host galaxy. We have selected a sample of nearby compact radio sources, unbiased by radio spectrum, to determine their radio luminosity function, size distribution, dynamical ages, and emission line properties in a complete and homogeneous way. First results indicate that the large majority of objects (>80%) exhibit classical GPS/CSS radio spectra, and show structures consistent with the being compact double, or compact symmetric objects. This sample provides and ideal basis to further test and constrain possible evolution scenarios, and to investigate the relation between radio spectra and morphologies, orientation and Doppler boosting in samples of young radio-loud AGN, in an unbiased way.Comment: LaTeX, 8 pages, 3 figs: Accepted by Publications of the Astronomical Society of Australia, as part of the proceedings of the 3rd GPS/CSS workshop, eds. T. Tzioumis et a

VLT and NTT Observations of Two EIS Cluster Candidates. Detection of the Early-Type Galaxies Sequence at z~1

Optical data from the ESO VLT-UT1 Science Verification observations are combined with near-infrared data from SOFI at the NTT to obtain optical-infrared color-magnitude diagrams for the objects in the fields of two EIS cluster candidates. In both cases, evidence is found for a well-defined sequence of red galaxies that appear to be significantly more clustered than the background population. These results suggest that the two systems are real physical associations. The (R-Ks), (I-Ks) and (J-Ks) colors of the red sequences are used, in conjunction with similar data for spectroscopically confirmed clusters, to obtain redshift estimates of z ~ 0.9 and z ~ 1.0 for these two systems. These results make these EIS cluster candidates prime targets for follow-up spectroscopic observations to confirm their reality and to measure more accurately their redshift.Comment: 6 pages, 5 figures, to appear in Astronomy & Astrophysics (Special Letters Edition on "First Science with the VLT"

Confirming EIS Clusters. Optical and Infrared Imaging

Clusters of galaxies are important targets in observationally cosmology, as they can be used both to study the evolution of the galaxies themselves and to constrain cosmological parameters. Here we report on the first results of a major effort to build up a sample of distant galaxy clusters to form the basis for further studies within those fields. We search for simultaneous overdensities in color and space to obtain supporting evidence for the reality of the clusters. We find a confirmation rate for EIS clusters of 66%, suggesting that a total of about 80 clusters with z>=0.6 are within reach using the EIS cluster candidates.Comment: 4 pages, 2 figures, to appear in the proceedings of the IGRAP International Conference 1999 on 'Clustering at high Redshift

Observations of the bright radio sources in the North Celestial Pole region at the RATAN-600 radio telescope

A survey of the North Celestial Pole region using the RATAN-600 radio telescope at five frequencies in the range 2.3 to 21.7 GHz is described. Sources were chosen from the NVSS catalogue. The flux densities of 171 sources in the Declination range +75 to +88 are presented; typical flux density errors are 5-10 percent including calibration errors. About 20 percent of the sources have flat spectra or a flat component.Comment: 21 pages, 7 figures; to be published in Astronomy and Astrophysics (without last figure with the spectra of the observed sources

An elusive radio halo in the merging cluster Abell 781?

Deep radio observations of the galaxy cluster Abell 781 have been carried out using the Giant Metrewave Radio Telescope at 325 MHz and have been compared to previous 610 MHz observations and to archival VLA 1.4 GHz data. The radio emission from the cluster is dominated by a diffuse source located at the outskirts of the X-ray emission, which we tentatively classify as a radio relic. We detected residual diffuse emission at the cluster centre at the level of S(325 MHz)~15-20 mJy. Our analysis disagrees with Govoni et al. (2011), and on the basis of simple spectral considerations we do not support their claim of a radio halo with flux density of 20-30 mJy at 1.4 GHz. Abell 781, a massive and merging cluster, is an intriguing case. Assuming that the residual emission is indicative of the presence of a radio halo barely detectable at our sensitivity level, it could be a very steep spectrum source.Comment: 5 pages, 4 figures, 1 table - Accepted for publication on Monthly Notices of the Royal Astronomical Society Letter

A new sample of faint Gigahertz Peaked Spectrum radio sources

The Westerbork Northern Sky Survey (WENSS) has been used to select a sample of Gigahertz Peaked Spectrum (GPS) radio sources at flux densities one to two orders of magnitude lower than bright GPS sources investigated in earlier studies. Sources with inverted spectra at frequencies above 325 MHz have been observed with the WSRT at 1.4 and 5 GHz and with the VLA at 8.6 and 15 GHz to select genuine GPS sources. This has resulted in a sample of 47 GPS sources with peak frequencies ranging from ~500 MHz to >15 GHz, and peak flux densities ranging from ~40 to ~900 mJy. Counts of GPS sources in our sample as a function of flux density have been compared with counts of large scale sources from WENSS scaled to 2 GHz, the typical peak frequency of our GPS sources. The counts can be made similar if the number of large scale sources at 2 GHz is divided by 250, and their flux densities increase by a factor of 10. On the scenario that all GPS sources evolve into large scale radio sources, these results show that the lifetime of a typical GPS source is ~250 times shorter than a typical large scale radio source, and that the source luminosity must decrease by a factor of ~10 in evolving from GPS to large scale radio source. However, we note that the redshift distributions of GPS and large scale radio sources are different and that this hampers a direct and straightforward interpretation of the source counts. Further modeling of radio source evolution combined with cosmological evolution of the radio luminosity function for large sources is required.Comment: LaTeX, 15 pages, 8 figs. To be published in A&AS. For more info see http://www.ast.cam.ac.uk/~snelle