The B3-Vla CSS sample. III: Evn & Merlin images at 18 cm

EVN and MERLIN observations at 18 cm are presented for 18 Compact Steep--spectrum radio Sources (CSSs) from the B3-VLA CSS sample. These sources were marginally resolved in previous VLA A-configuration observations at 4.9 and 8.4 GHz or had peculiar morphologies, two of them looking like core-jets. The MERLIN images basically confirm the VLA structures at 8.4 GHz while the EVN and/or the combined images reveal several additional details.Comment: 17 pages, many low resoltion figures, A&A accepted. A higher resolution gzipped postscript file can be found at http://www.ira.cnr.it/~ddallaca/h3443.ps.g

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 radio 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 presence 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 earlier activity.Comment: 18 paged, 18 figures, accepted for publication on A&

Data display and analysis

Graphical character recognizer and data displa

Optical identifications of High Frequency Peakers

We present CCD observations of 13 objects from a complete sample of 55 bright High Frequency Peaker (HFP) radio sources, and provide optical identification for 12 of them. Images in R and V filters have been used to derive some additional information concerning the host of the radio source. Three hosts are likely to be galaxies, one resulted slightly extended, while the remaining 8 are likely distant quasars. Based on these identifications and those available in the literature, we find that the fraction of quasars in our HFP sample is significantly higher than in samples of Compact Steep-Spectrum and GHz-Peaked Spectrum radio sources.Comment: 7 pages, A&A accepte

Parsec-scale morphology and spectral index distribution in faint high frequency peakers

We investigate the parsec-scale structure of 17 high frequency peaking radio sources from the faint HFP sample. VLBA observations were carried out at two adjacent frequencies, 8.4 and 15.3 GHz, both in the optically-thin part of the spectrum, to obtain the spectral index information. We found that 64% of the sources are resolved into subcomponents, while 36% are unresolved even at the highest frequency. Among the resolved sources, 7 have a morphology and a spectral index distribution typical of young radio sources, while in other 4 sources, all optically associated with quasars, the radio properties resemble those of the blazar population. The equipartition magnetic field of the single components are a few tens milliGauss, similar to the values found in the hotspots of young sources with larger sizes. Such high magnetic fields cause severe radiative losses, precluding the formation of extended lobe structures emitting at centimeter wavelengths. The magnetic fields derived in the various components of individual source are usually very different, indicating a non self-similar source evolution, at least during the very first stages of the source growth.Comment: 14 pages, 5 figures, accepted for publication in MNRA

VLBI images at 327 MHz of compact steep spectrum and GHz-peaked spectrum sources from the 3C and PW samples

We present results on global very long baseline interferometry (VLBI) observations at 327 MHz of 18 compact steep-spectrum (CSS) and GHz-peaked spectrum (GPS) radio sources from the 3C and the Peacock & Wall catalogues. About 80 per cent of the sources have a 'double/triple' structure. The radio emission at 327 MHz is dominated by steep-spectrum extended structures, while compact regions become predominant at higher frequencies. As a consequence, we could unambiguously detect the core region only in three sources, likely due to self-absorption affecting its emission at this low frequency. Despite their low surface brightness, lobes store the majority of the source energy budget, whose correct estimate is a key ingredient in tackling the radio source evolution. Low-frequency VLBI observations able to disentangle the lobe emission from that of other regions are therefore the best way to infer the energetics of these objects. Dynamical ages estimated from energy budget arguments provide values between 2 × 103 and 5 × 104 yr, in agreement with the radiative ages estimated from the fit of the integrated synchrotron spectrum, further supporting the youth of these objects. A discrepancy between radiative and dynamical ages is observed in a few sources where the integrated spectrum is dominated by hotspots. In this case the radiative age likely represents the time spent by the particles in these regions, rather than the source age

Physical parameters in the hot spots and jets of Compact Symmetric Objects

We present a model to determine the physical parameters of jets and hot spots of a sample of CSOs under very basic assumptions like synchrotron emission and minimum energy conditions. Based on this model we propose a simple evolutionary scenario for these sources assuming that they evolve in ram pressure equilibrium with the external medium and constant jet power. The parameters of our model are constrained from fits of observational data (radio luminosity, hot spot radius and hot spot advance speed) versus projected linear size. From these plots we conclude that CSOs evolve self-similarly and that their radio luminosity increases with linear size along the first kiloparsec. Assuming that the jets feeding CSOs are relativistic from both kinematical and thermodynamical points of view, we use the values of the pressure and particle number density within the hot spots to estimate the fluxes of momentum (thrust), energy, and particles of these relativistic jets. The mean jet power obtained in this way is within an order of magnitude that inferred for FRII sources, which is consistent with CSOs being the possible precursors of large doubles. The inferred flux of particles corresponds to, for a barionic jet, about a 10% of the mass accreted by a black hole of $10^8 {\rm M_{\odot}}$ at the Eddington limit, pointing towards a very efficient conversion of accretion flow into ejection, or to a leptonic composition of jets.Comment: 11 pages, 2 figures. Accepted for publication in Astrophysical Journa

A sample of small size 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.Comment: 17 pages, 15 figures, accepted for publication in MNRA

Multi-frequency VLBA observations of compact sources from the Peacock & Wall catalogue

VLBA observations are presented for 6 compact radio sources selected from the Peacock & Wall catalogue. From the new morphological and spectral information 2 objects that in the Peacock and Wall catalogue are flat spectrum (alpha < 0.5) sources, appear to be double sided objects with linear sizes of the order of one kpc. Three are core-jet sources and the last one is still an ``enigmatic'' object. These data complete the sample of small double compact sources in the Peacock & Wall catalogue and the complete list is given.Comment: 11 pages, 14 figures, aa.cls Accepted by A&

Spectral variability in faint high frequency peakers

We present the analysis of simultaneous multi-frequency Very Large Array (VLA) observations of 57 out of 61 sources from the ``faint'' high frequency peaker (HFP) sample carried out in various epochs. Sloan Digital Sky Survey (SDSS) data have been used to identify the optical counterpart of each radio source. From the analysis of the multi-epoch spectra we find that 24 sources do not show evidence of spectral variability, while 12 objects do not possess a peaked spectrum anymore at least in one of the observing epochs. Among the remaining 21 sources showing some degree of variability, we find that in 8 objects the spectral properties change consistently with the expectation for a radio source undergoing adiabatic expansion. The comparison between the variability and the optical identification suggests that the majority of radio sources hosted in galaxies likely represent the young radio source population, whereas the majority of those associated with quasars are part of a different population similar to flat-spectrum objects, which possess peaked spectra during short intervals of their life, as found in other samples of high-frequency peaking objects. The analysis of the optical images from the SDSS points out the presence of companions around 6 HFP hosted in galaxies, suggesting that young radio sources resides in groups.Comment: 16 pages, 5 figures; accepted for publication in MNRA