Spectroscopy of radio sources from the third Bologna survey

We present long-slit CCD spectroscopy of eleven optical candidates for selected radio sources from the third Bologna survey (B3). One object (0141+398) is a probable misidentification, a foreground star. The remaining ones are a mixture of quasars and active galaxies, ranging in redshift from 0.11 to 0.85. B3 0219+443 is a steep-spectrum quasar. B3 1141+374 is identified with an interacting galaxy pair, with the southern component harboring an active nucleus

A project for polarimetric observations in single dish with Medicina and Noto 32 m antennas

A project with multidisciplinary characteristics, aimed to implement the possibility of polarimetric measurements in single dish at the VLBI stations of Medicina and Noto, is presented. The project will open a new window on many astrophysical items that may be approached using the already existing instrumentation and facilities of the two Italian radioastronomical stations. We report here some scientific backgrounds, together with some technical evaluations, on which the feasibility of the project is based

Spectroscopy of radio sources from the third Bologna survey

We present long-slit CCD spectroscopy of eleven optical candidates for selected radio sources from the third Bologna survey (B3). One object (0141+398) is a probable misidentification, a foreground star. The remaining ones are a mixture of quasars and active galaxies, ranging in redshift from 0.11 to 0.85. B3 0219+443 is a steep-spectrum quasar. B3 1141+374 is identified with an interacting galaxy pair, with the southern component harboring an active nucleus

Radio-optically selected clusters of galaxies. I. The radiogalaxy sample

In order to study the status and the possible evolution of clusters of galaxies at intermediate redshifts (z ~ 0.1 - 0.3), as well as their spatial correlation and relationship with the local environment, we built a sample of candidate groups and clusters of galaxies using radiogalaxies as tracers of dense environments. This technique - complementary to purely optical or X-ray cluster selection methods - represents an interesting tool for the selection of clusters in a wide range of richness, so to make it possible to study the global properties of groups and clusters of galaxies, such as their morphological content, dynamical status and number density, as well as the effect of the environment on the radio emission phenomena. In this paper we describe the compilation of a catalogue of 16000 radio sources in the region of the South Galactic Pole extracted from the publicly available NRAO VLA Sky Survey maps, and the optical identification procedure with galaxies brighter than b_J=20.0 in the EDSGC Catalogue. The radiogalaxy sample, valuable for the study of radio source populations down to low flux levels, consists of 1288 identifications and has been used to detect candidate groups and clusters associated to NVSS radio sources. In a companion paper we will discuss the cluster detection method, the cluster sample as well as first spectroscopic results.Comment: 15 pages, 6 Postscript and 1 GIF figures. Accepted for publication in A&

Radio-optically selected clusters of galaxies. II. The cluster sample

We present a sample of 171 candidate groups and clusters of galaxies at intermediate redshift over an area of ~550 square degrees at the South Galactic Pole selected by using optically identified radio sources from the NRAO VLA Sky Survey as tracers of dense environment. Out of these 171 candidates, 76 have a counterpart in the literature while 95 of them are previously unknown clusters. This paper presents the cluster selection technique, based on the search of excesses in the optical surface density of galaxies near identified radiogalaxies, and the first spectroscopic results aimed to confirm the presence of a cluster. Spectroscopy for 11 candidates led to the detection of 9 clusters at redshift in the range 0.13 - 0.3, with estimated velocity dispersions ranging from values typical of clusters to those of galaxy groups. These results show that this technique represents a powerful tool for the selection of homogeneous samples of intermediate redshift clusters over a wide range of richness.Comment: 13 pages, 3 Postscript and 2 GIF figures. Accepted for publication in A&

The contribution of the Unresolved Extragalactic Radio Sources to the Brightness Temperature of the sky

The contribution of the Unresolved Extragalactic Radio Sources to the diffuse brightness of the sky was evaluated using the source number - flux measurements available in literature. We first optimized the fitting function of the data based on number counts distribution. We then computed the brightness temperature at various frequencies from 151 MHz to 8440 MHz and derived its spectral dependence. As expected the frequency dependence can be described by a power law with a spectral index $\gamma \simeq -2.7$, in agreement with the flux emitted by the {\it steep spectrum} sources. The contribution of {\it flat spectrum} sources becomes relevant at frequencies above several GHz. Using the data available in literature we improved our knowledge of the brightness of the unresolved extragalactic radio sources. The results obtained have general validity and they can be used to disentangle the various contributions of the sky brightness and to evaluate the CMB temperature.Comment: Accepted for publication in the Astrophysical Journa