C. Fanti

Extended emission around GPS radio sources

Extended radio emission detected around a sample of GHz Peaked Spectrum (GPS) radio sources is discussed. Evidence for extended emission which is related to the GPS source is found in 6 objects out of 33. Three objects are associated with quasars with core-jet pc-scale morphology, and three are identified with galaxies with symmetric (CSO) radio morphology. We conclude that the core-jet GPS quasars are likely to be beamed objects with a continuous supply of energy from the core to the kpc scale. It is also possible that low surface brightness extended rad io emission is present in other GPS quasars but the emission is below our detection limit due to the high redshifts of the objects. On the other hand, the CSO/galaxies with extended large scale emission may be rejuvenated sources where the extended emission is the relic of previous activity. In general, the prese nce of large scale emission associated with GPS galaxies is uncommon, suggesting that in the context of the recurrent activity model, the time scale between subsequent bursts is in general longer than the radiative lifetime of the radio emission from the e arlier activity (� 10 8 yrs).

The B3-VLA CSS sample - VII. WSRT polarisation observations and the ambient Faraday medium properties revisited

We present new polarisation observations at 13 cm, acquired using the Westerbork Synthesis Radio Telescope (WSRT), of 65 sources, from the B3-VLA sample of Compact Steep-Spectrum sources. These new data are combined with our VLA polarisation data, at 3.6, 6 and, 21 cm, presented in a previous paper. Due to the multi-channel frequency capabilities of the WSRT, these new 13 cm observations enable a more reliable determination of integrated Rotation Measures, and of depolarisation behaviour with wavelength. The new data are inconsistent with the depolarisation models that we used earlier, and we propose an alternative model which seems to work properly. We also revise our previous model for the external Faraday screen, and its dependence on the source redshift.

High redshift X-ray galaxy clusters II. The LX-T relationship revisited

Aims. In this paper we re-visit the observational relation between X-ray luminosity and temperature for high-z galaxy clusters and compare it with the local LX–T and with theoretical models. Methods. To these ends we use a sample of 17 clusters extracted from the Chandra archive supplemented with additional clusters from the literature, either observed by Chandra or XMM–Newton, to form a final sample of 39 high redshift (0.25 < z < 1.3) objects. Different statistical approaches are adopted to analyze the LX–T relation. Results. The slope of the LX–T relation of high redshift clusters is steeper than expected from the self-similar model predictions and steeper, even though still compatible within the errors, than the local LX–T slope. The distant cluster LX–T relation shows a significant evolution with respect to the local Universe: high-z clusters are more luminous than the local ones by a factor ≈ 2a t any given temperature. The evolution with redshift of the LX–T relation cannot be described by a single power law nor by the evolution predicted by the self-similar model. Conclusions. We find a strong evolution, similar or stronger than the self-similar model, from z = 0t oz ≤ 0. 3f ollowed by a much weaker, if any, evolution at higher redshifts. The weaker evolution is compatible with non-gravitational models of structure formation. According to us a statistically significant sample of nearby clusters (z < 0.25) should be observed with the current available X-ray telescopes to completely exclude observational effects due to different generation detectors and to understand this novel result.

A sample of small-sized compact steep-spectrum radio sources: VLBI images and VLA polarization at 5 GHz

Global VLBI observations at 5 GHz have been performed to study the source morphology in 10 compact steep-spectrum (CSS) sources selected from the Peacock & Wall catalogue with the aim of finding asymmetric structures produced by the interaction with the ambient medium. The combination of these data and earlier 1.7-GHz observations allows the study of the spectral index distribution across the source structure and the unambiguous determination of the nature of each component. In seven sources we detected the core component with a flat or inverted spectrum. In six sources the radio emission has a two-sided morphology and comes mainly from steep-spectrum extended structures, like lobes, jets, and hotspots. Only one source, 0319+121, has a one-sided core-jet structure. In three out of the six sources with a two-sided structure the flux density arising from the lobes is asymmetric, and the brightest lobe is the one closest to the core, suggesting that the jets are expanding in an inhomogeneous ambient medium which may influence the source growth. The interaction between the jet and the environment may slow down the source expansion and enhance the luminosity due to severe radiative losses, likely producing an excess of CSS radio sources in flux density limited samples. The lobes of the other three asymmetric sources have a brighter-when-farther behaviour, in agreement with what is expected by projection and relativistic effects. Simultaneous VLA observations carried out to investigate the polarization properties of the targets detected significant polarized emission (~5.5%) only from the quasar 0319+121.

High redshift X-ray galaxy clusters I. The impact of point sources on the cluster properties

Context. The current generation of X-ray observatories like Chandra allows studies with very fine spatial details. It is now possible to resolve X-ray point sources projected into the cluster diffuse emission and exclude them from the analysis to estimate the “correct” X-ray observables. Aims. We wish to verify the incidence of point sources on the cluster thermal emission and to evaluate the impact of their non-thermal emission on the determination of cluster properties. Methods. To these ends we use a sample of 18 high-z (0.25 0.7 where temperature and luminosity increase up to 24% and 22%, respectively. Conclusions. The conclusions are that point sources should be removed to correctly estimate the cluster properties. However the inclusion of the point sources does not impact significantly the slope and normalization of the Lbol–T relationship since for each cluster the correction to be applied to T and Lbol produces a moderate shift in the Lbol–T plane almost parallel to the best-fit of the “correct” Lbol–T relation.

The B3-VLA CSS sample. VI. VLA images at 2 cm

Aims. New radio observations are presented for a sample of 56 Compact Steep Spectrum (CSS) radio sources from the B3-VLA CSS sample. Methods. We used the VLA A-configuration observation at 2 cm to obtain high-frequency, high-resolution data. Results. The majority (85%) of sources have a double morphology with a number of them showing a large asymmetry in terms of their component flux densities and/or component arm ratio. These new data have revealed 27 cores and core candidates. Three of the sources have a core-jet morphology and the morphologies of a few objects (≤10%) are still ambiguous. The integrated radio spectra, over a frequency range from 0.16 to 15 GHz, show good agreement with a continuous injection model for >85% of the sources.We present new polarisation observations at 13 cm, acquired using the Westerbork Synthesis Radio Telescope (WSRT), of 65 sources, from the B3-VLA sample of Compact Steep-Spectrum sources. These new data are combined with our VLA polarisation data, at 3.6, 6 and, 21 cm, presented in a previous paper. Due to the multi-channel frequency capabilities of the WSRT, these new 13 cm observations enable a more reliable determination of integrated Rotation Measures, and of depolarisation behaviour with wavelength. The new data are inconsistent with the depolarisation models that we used earlier, and we propose an alternative model which seems to work properly. We also revise our previous model for the external Faraday screen, and its dependence on the source redshift.

The B3-VLA CSS sample VIII. New optical identifications from the Sloan Digital Sky Survey The ultraviolet-optical spectral energy distribution of the young radio sources

Compact steep-spectrum radio sources and giga-hertz peaked spectrum radio sources (CSS/GPS) are generally considered to be mostly young radio sources. In recent years we studied at many wavelengths a sample of these objects selected from the B3-VLA catalog: the B3-VLA CSS sample. Only ~ 60 % of the sources were optically identified. We aim to increase the number of optical identifications and study the properties of the host galaxies of young radio sources. We cross-correlated the CSS B3-VLA sample with the Sloan Digital Sky Survey (SDSS), DR7, and complemented the SDSS photometry with available GALEX (DR 4/5 and 6) and near-IR data from UKIRT and 2MASS. We obtained new identifications and photometric redshifts for eight faint galaxies and for one quasar and two quasar candidates. Overall we have 27 galaxies with SDSS photometry in five bands, for which we derived the ultraviolet-optical spectral energy distribution (UV-O-SED). We extended our investigation to additional CSS/GPS selected from the literature. Most of the galaxies show an excess of ultra-violet (UV) radiation compared with the UV-O-SED of local radio-quiet ellipticals. We found a strong dependence of the UV excess on redshift and analyzed it assuming that it is generated either from the nucleus (hidden quasar) or from a young stellar population (YSP). We also compare the UV-O-SEDs of our CSS/GPS sources with those of a selection of large size (LSO) powerful radio sources from the literature. If the major process of the UV excess is caused by a YSP, our conclusion is that it is the result of the merger process that also triggered the onset of the radio source with some time delay. We do not see evidence for a major contribution from a YSP triggered by the radio sources itself.