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We have used the available samples of Gigahertz Peaked Spectrum (GPS) galaxies to investigate their evolution properties in the framework of the “youth” scenario. Care was taken to properly allow for the different selection criteria used to define the samples. We find that the observed redshift and peak frequency distributions can be satisfactorily accounted for in terms of simple luminosity evolution of individual sources, along the lines discussed by Fanti et al. (1995, A&A, 302, 317) and Begelman (1996, in Proc. Cygnus A, Study of Radio Galaxy; 1999, in Proc. of KNAW Colloq.), although the derived parameter values have large uncertainties due to ambiguities in the selection of GPS sources and to the incompleteness of redshift measurements. However the simplest self-similar model, whereby the evolution is controlled only by the radial profile of the density of the ambient medium is not good enough and one additional parameter needs to be introduced. The fit requires a decrease of the emitted power and of the peak luminosity with source age or with decreasing peak frequency, at variance with the Snellen et al. (2000, MNRAS, 319, 445) model. On the other hand, our analysis confirms the rather flat slope of the luminosity function, found by Snellen et al. (2000) who also report indications of a high luminosity break, not required by the data sets we have used. Our results suggest that the GPS galaxies are the precursors of extended radio sources with luminosities below the break of the luminosity function. No cosmological evolution of the GPS galaxy population is required by presently available data. more...

We present the results of VLBA observations at 6 and 3.6 cm for eighteen Compact Steep Spectrum radio sources (CSS) from the B3-VLA CSS sample. In most cases these VLBA images display a “Double/Triple” morphology, and the core is unambiguously detected in seven sources. Multifrequency images allow us to study the spectral properties of the individual source components and to constrain the spectral age. In lobe-dominated sources the radiative ages deduced from the synchrotron theory are in the range of up $5\times 10 ^{3}$years, if equipartition magnetic field is assumed. Polarized emission is detected at a few percent level for two sources only. They were the only two sources displaying polarized emission in VLA A configuration data, and this implies that beam depolarization is not effective in reducing the integrated fractional polarization for these sources. more...

VLBA observations at 18 cm are presented for 28 Compact Steep–spectrum radio Sources (CSSs) from the B3–VLA CSS sample. These sources were unresolved in previous VLA observations at high frequencies or their brightness distribution was dominated by an unresolved steep spectrum component. More than half of them also showed a low frequency turnover in their radio spectrum. The VLBA images display in most cases a compact symmetric structure. Only in a minority of cases complex morphologies are present. more...

We present WSRT and VLA radio observations of the neutral hydrogen in the radio galaxy Coma A. We detect extended $\ion{H}{I}$absorption against both radio lobes of Coma A, at distances of about 30 kpc from the centre. Coma A is the first radio galaxy in which $\ion{H}{I}$is seen in absorption at such large distances from the nucleus. The match between the velocities of the neutral hydrogen and those of the extended ionized gas suggests that they are part of the same disk-like structure of at least 60 kpc in diameter. Most likely, this gas disk is partly ionised by the bulk motion of the radio lobes expanding into it. The gas mass of this disk is at least 109$M_\odot$. The relatively regular structure of the gas disk suggests that a merger occurred involving at least one large gas-rich galaxy, at least a few times 108yr ago. more...

The submillimetre-wave spectrum of the molecular ions N15NH+, 15NNH+, N15ND+, and 15NND+have been investigated in the laboratory using a source-modulation microwave spectrometer equipped with a negative glow discharge cell. The diazenylium ion was produced in a Ar/N2/H2(D2) discharge plasma and the 15N-containing isotopologues were observed in natural abundance. Six new rotational transitions for the protonated species and seven for the deuterated ones were accurately measured in the frequency range 270-760?GHz. These new laboratory measurements of the rare isotopologues of N2H+provide very precise rest frequencies at millimetre and submillimetre wavelengths useful for the radioastronomical identification of their rotational lines in the ISM. more...

We propose a morphological classification based on the parsec scale structure of fifty-one High Frequency Peakers (HFPs) from the ?bright? HFP sample. VLBA images at two adjacent frequencies (chosen among?8.4, 15.3, 22.2 and 43.2?GHz) have been used to investigate the morphological properties of the HFPs in the optically thin part of their spectrum. We confirm that there is quite a clear distinction between the pc-scale radio structure of galaxies and quasars: the?78% of the galaxies show a ?Double/Triple? morphology, typical of Compact Symmetric Objects (CSOs), while the?87% of the quasars are characterised by Core-Jet or unresolved structure. This suggests that most HFP candidates identified with quasars are likely blazar objects in which a flaring self-absorbed component at the jet base was outshining the remainder of the source at the time of the selection based on the spectral shape.?Among the sources classified as CSOs or candidates it is possible to find extremely young radio sources with ages of about 100?years or even?less. more...

We present new, simultaneous, multifrequency observations of 45 out of the 55 candidate High Frequency Peakers (HFP) selected by Dallacasa et al. ([CITE]), carried out 3 to 4 years after a first set of observations. Our sub-sample consists of 10 galaxies, 28 stellar objects (”quasars”) and 7 unidentified sources. Both sets of observations are sensitive enough to allow the detection of variability at the 10% level or lower. While galaxies do not show significant variability, most quasars do. Seven of them no longer show the convex spectrum which is the defining property of Gigahertz Peaked Spectrum (GPS)/HFP sources and are interpreted as blazars caught by Dallacasa et al. ([CITE]) during a flare, when a highly self-absorbed component dominated the emission. In general, the variability properties (amplitude, timescales, correlation between peak luminosity and peak frequency of the flaring component) of the quasar sub-sample resemble those of blazars. We thus conclude that most HFP candidates identified with quasars may well be flaring blazars. more...