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Register a new userMulti-frequency polarimetry of a complete sample of PACO radio sources
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We present high sensitivity polarimetric observations in 6 bands covering the 5.5-38 GHz range of a complete sample of 53 compact extragalactic radio sources brighter than 200 mJy at 20 GHz. The observations, carried out with the Australia Telescope Compact Array (ATCA), achieved a 91% detection rate (at 5 sigma). Within this frequency range the spectra of about 95% of sources are well fitted by double power laws, both in total intensity and in polarisation, but the spectral shapes are generally different in the two cases. Most sources were classified as either steep- or peaked-spectrum but less than 50% have the same classification in total and in polarised intensity. No significant trends of the polarisation degree with flux density or with frequency were found. The mean variability index in total intensity of steep-spectrum sources increases with frequency for a 4-5 year lag, while no significant trend shows up for the other sources and for the 8 year lag. In polarisation, the variability index, that could be computed only for the 8 year lag, is substantially higher than in total intensity and has no significant frequency dependence.
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We present high sensitivity ($sigma_P simeq 0.6,$mJy) polarimetric observations in seven bands, from $2.1$ to $38,$GHz, of a complete sample of $104$ compact extragalactic radio sources brighter than $200,$mJy at $20,$GHz. Polarization measurements in six bands, in the range $5.5-38,$GHz, for $53$ of these objects were reported by citet{Galluzzi2017}. We have added new measurements in the same six bands for another 51 sources and measurements at $2.1,$GHz for the full sample of $104$ sources. Also, the previous measurements at $18$, $24$, $33$ and $38,$GHz were re-calibrated using the updated model for the flux density absolute calibrator, PKS1934-638, not available for the earlier analysis. The observations, carried out with the Australia Telescope Compact Array (ATCA), achieved a $90%$ detection rate (at $5sigma$) in polarization. $89$ of our sources have a counterpart in the $72$ to $231,$MHz GLEAM survey citep{HurleyWalker2017}, providing an unparalleled spectral coverage of $2.7$ decades of frequency for these sources. While the total intensity data from $5.5$ to $38,$GHz could be interpreted in terms of single component emission, a joint analysis of more extended total intensity spectra presented here, and of the polarization spectra, reveals that over $90%$ of our sources show clear indications of at least two emission components. We interpret this as an evidence of recurrent activity. Our high sensitivity polarimetry has allowed a $5,sigma$ detection of the weak circular polarization for $sim 38%$ of the dataset, and a deeper estimate of $20,$GHz polarization source counts than has been possible so far.
We present Atacama Large Millimeter/submillimiter Array (ALMA) high sensitivity ($sigma_P simeq 0.4,$mJy) polarimetric observations at $97.5,$GHz (Band 3) of a complete sample of $32$ extragalactic radio sources drawn from the faint Planck-ATCA Co-eval Observations (PACO) sample ($b<-75^circ$, compact sources brighter than $200,$mJy at $20,$GHz). We achieved a detection rate of $~97%$ at $3,sigma$ (only $1$ non-detection). We complement these observations with new Australia Telescope Compact Array (ATCA) data between $2.1$ and $35,$GHz obtained within a few months and with data published in earlier papers from our collaboration. Adding the co-eval GaLactic and Extragalactic All-sky Murchison widefield array (GLEAM) survey detections between $70,$ and $230,$MHz for our sources, we present spectra over more than $3$ decades in frequency in total intensity and over about $1.7$ decades in polarization. The spectra of our sources are smooth over the whole frequency range, with no sign of dust emission from the host galaxy at mm wavelengths nor of a sharp high frequency decline due, for example, to electron ageing. We do however find indications of multiple emitting components and present a classification based on the number of detected components. We analyze the polarization fraction behaviour and distributions up to $97,$GHz for different source classes. Source counts in polarization are presented at $95,$GHz.
We report multi-frequency circular polarization measurements for the four extragalactic radio sources 0056-00, 0716+71, 3C138 and 3C161 taken at the Effelsberg 100-m radiotelescope. The data reduction is based on a new calibration procedure that allows the contemporary measurement of the four Stokes parameters at different frequencies with single-dish radiotelescopes. We are in the process of framing the observed full Stokes spectra within a theoretical model that explains that the level of measured circular polarization as Faraday conversion.
Non-thermal properties of galaxy clusters have been studied with detailed and deep radio images in comparison with X-ray data. While much progress has been made, most of the studied clusters are at a relatively low redshift (z < 0.3). We here investigate the evolutionary properties of the non-thermal cluster emission using two statistically complete samples at z > 0.3. We obtained short JVLA observations at L-band of the statistically complete sample of very X-ray luminous clusters from the Massive Cluster Survey (MACS) presented by Ebeling et al. (2010), and redshift range 0.3 - 0.5. We add to this list the complete sample of the 12 most distant MACS clusters (z > 0.5) presented in Ebeling et al. (2007). Most clusters show evidence of emission in the radio regime. We present the radio properties of all clusters in our sample and show images of newly detected diffuse sources. A radio halo is detected in 19 clusters, and five clusters contain a relic source. Most of the brightest cluster galaxies (BCG) in relaxed clusters show radio emission with powers typical of FRII radio galaxies, and some are surrounded by a radio mini-halo. The high frequency of radio emission from the BCG in relaxed clusters suggests that BCG feedback mechanisms are in place already at z about 0.6. The properties of radio halos and the small number of detected relics suggest redshift evolution in the properties of diffuse sources. The radio power (and size) of radio halos could be related to the number of past merger events in the history of the system. In this scenario, the presence of a giant and high-power radio halo is indicative of an evolved system with a large number of past major mergers.
We observed with the VLBA at 2.3 and 8.6 GHz a complete flux-density limited sample of 482 radio sources with declination >+75 degrees brighter than 200 mJy at 1.4 GHz drawn from the NVSS catalog. 34% of the sources show parsec-scale emission above the flux density detection limit of 30 mJy; their accurate positions and parsec-scale structure parameters are determined. Among all the sources detected at least at the shortest VLBA baselines, the majority, or 72%, has a steep single-dish spectrum. The fraction of the sources with a detectable parsec-scale structure is above 95% among the flat-spectrum and close to 25% among the steep-spectrum objects. We identified 82 compact steep-spectrum source candidates, which make up 17% of the sample; most of them are reported for the first time. The compactness and the brightness temperature of the sources in our sample show a positive correlation with single-dish and VLBA spectral indices. All the sources with a significant 8 GHz variability were detected by the VLBA snapshot observations, which independently confirmed their compactness. We demonstrated that 54% of the sources detected by the VLBA at 2.3 GHz in our sample have a steep VLBA spectrum. The compact radio emission of these sources is likely dominated by optically thin jets or mini-lobes, not by an opaque jet core. These results show that future VLBI surveys aimed to search for new sources with parsec-scale structure should include not only flat-spectrum sources, but also steep-spectrum ones in order to reach an acceptable level of completeness.
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