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

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

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

Contribution to the Diffuse Radio Background from Extragalactic Radio Sources

We examine the brightness of the Cosmic Radio Background (CRB) by comparing the contribution from individual source counts to absolute measurements. We use a compilation of radio counts to estimate the contribution of detected sources to the CRB in several different frequency bands.We apply a Monte Carlo Markov Chain technique to estimate the brightness values and uncertainties, paying attention to various sources of systematic error. We compare our results to absolute measurements from the ARCADE 2 experiment. At v = 150 MHz, 325 MHz, 408 MHz, 610 MHz, 1.4 GHz, 4.8 GHz, and 8.4 GHz our calculated contributions to the background sky temperature are 18, 2.8, 1.6, 0.71, 0.11, 0.0032, 0.0059 K, respectively. If the ARCADE 2 measurements are correct and come from sources, then there must be an additional population of radio galaxies, fainter than where current data are probing. More specifically, the Euclidean-normalized counts at 1.4 GHz have to have an additional bump below about 10 {\mu}Jy.Comment: 9 pages, 7 figures, 3 tables, accepted MNRA

CSSs in a sample of B2 radio sources of intermediate strength

We present radio observations of 19 candidate compact steep-spectrum (CSS) objects selected from a well-defined, complete sample of 52 B2 radio sources of intermediate strength. These observations were made with the VLA A-array at 4.835 GHz. The radio structures of the entire sample are summarised and the brightness asymmetries within the compact sources are compared with those of the more extended ones, as well as with those in the 3CRR sample and the CSSs from the B3-VLA sample. About 25 per cent of the CSS sources exhibit large brightness asymmetries, with a flux density ratio for the opposing lobes of $>$5, possibly due to interaction of the jets with infalling material. The corresponding percentage for the larger-sized objects is only about 5 per cent. We also investigate possible dependence of the flux density asymmetry of the lobes on redshift, since this might be affected by more interactions and mergers in the past. No such dependence is found. A few individual objects of interest are discussed in the paper.Comment: 10 pages, 7 figures, 2 tables; accepted for publication in Astronomy and Astrophysic

Sources of the Radio Background Considered

We investigate different scenarios for the origin of the extragalactic radio background. The surface brightness of the background, as reported by the ARCADE 2 collaboration, is several times higher than that which would result from currently observed radio sources. We consider contributions to the background from diffuse synchrotron emission from clusters and the intergalactic medium, previously unrecognized flux from low surface brightness regions of radio sources, and faint point sources below the flux limit of existing surveys. By examining radio source counts available in the literature, we conclude that most of the radio background is produced by radio point sources that dominate at sub microJy fluxes. We show that a truly diffuse background produced by electrons far from galaxes is ruled out because such energetic electrons would overproduce the obserevd X-ray/gamma-ray background through inverse Compton scattering of the other photon fields. Unrecognized flux from low surface brightness regions of extended radio sources, or moderate flux sources missed entirely by radio source count surveys, cannot explain the bulk of the observed background, but may contribute as much as 10 per cent. We consider both radio supernovae and radio quiet quasars as candidate sources for the background, and show that both fail to produce it at the observed level because of insufficient number of objects and total flux, although radio quiet quasars contribute at the level of at least a few percent. We conclude that if the radio background is at the level reported, a majority of the total surface brightness would have to be produced by ordinary starforming galaxies above redshift 1 characterized by an evolving radio far-infrared correlation, which changes toward the radio loud with redshift.Comment: 12 pages, 3 figures, 1 table; MNRAS accepted and in press, (previously submitted ApJ but withdrawn before review

a deep radio and optical survey near the north galactic pole v jhk observations of a sample of 5c 12 optical identifications

n/

SPACECRAFT DOPPLER TRACKING WITH A VLBI ANTENNA

Accurate measurements of the Doppler shift of the Voyager 2 spacecraft (26 A.U.) have been performed in the period 23/7/88-12/8/88 with the 32 m VLBI antenna at Medicina (BO). The device which allows the use of VLBI instrumentation for precision Doppler tracking is basically an open- loop receiver and is called digital tone extractor (DTE). Simultaneous measurements were performed at NASA's Deep Space Network (DSN) stations of the Madrid complex, using a different technique (closed loop). In the most interesting tracking configuration, the signal was transmitted in S- band (2.1GHz) from the 70m DSN station at Canberra (Australia), retransmitted back coherently from the spacecraft in X-band (8.4 GHz-19W) and received 7h 6min later at Medicina and Madrid. The main purPose of the experiment was to test the capabilities of this new system and to character- ize its performances. This task has been successfully accomplished with the acquisition of high-quality data, which are presently under analysis. We plan also to compare and correlate the data with the ones acquired at Madrid stations, in order to separate out different noise contributions to the measured signal. The use of Medicina antenna as a listen-only station is planned for the gravitational wave experiment of the Ulysses spacecraft (ESA), in 1992