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We report the discovery of a double-double radio source (DDRS) J0028+0035. We observed it with LOFAR, GMRT, and the VLA. By combining our observational data with those from the literature, we gathered an appreciable set of radio flux density measurements covering the range from 74 MHz to 14 GHz. This enabled us to carry out an extensive review of physical properties of the source and its dynamical evolution analysis. In particular, we found that, while the age of the large-scale outer lobes is about 245 Myr, the renewal of the jet activity, which is directly responsible for the double-double structure, took place only about 3.6 Myr ago after about 11 Myr long period of quiescence. Another important property typical for DDRSs and also present here is that the injection spectral indices for the inner and the outer pair of lobes are similar. The jet powers in J0028+0035 are similar too. Both these circumstances support our inference that it is, in fact, a DDRS which was not recognized as such so far because of the presence of a coincident compact object close to the inner double so that the centre of J0028+0035 is apparently a triple., Comment: 14 pages, 8 figures, matches the version published in MNRAS

Cosmological simulations predict that an intergalactic magnetic field (IGMF) pervades the large scale structure (LSS) of the Universe. Measuring the IGMF is important to determine its origin (i.e. primordial or otherwise). Using data from the LOFAR Two Metre Sky Survey (LoTSS), we present the Faraday rotation measure (RM) and depolarisation properties of the giant radio galaxy J1235+5317, at a redshift of $z = 0.34$ and 3.38 Mpc in size. We find a mean RM difference between the lobes of $2.5\pm0.1$ rad/m$^2$ , in addition to small scale RM variations of ~0.1 rad/m$^2$ . From a catalogue of LSS filaments based on optical spectroscopic observations in the local universe, we find an excess of filaments intersecting the line of sight to only one of the lobes. Associating the entire RM difference to these LSS filaments leads to a gas density-weighted IGMF strength of ~0.3 {\mu}G. However, direct comparison with cosmological simulations of the RM contribution from LSS filaments gives a low probability (~5%) for an RM contribution as large as 2.5 rad/m$^2$ , for the case of IGMF strengths of 10 to 50 nG. It is likely that variations in the RM from the Milky Way (on 11' scales) contribute significantly to the mean RM difference, and a denser RM grid is required to better constrain this contribution. In general, this work demonstrates the potential of the LOFAR telescope to probe the weak signature of the IGMF. Future studies, with thousands of sources with high accuracy RMs from LoTSS, will enable more stringent constraints on the nature of the IGMF., Comment: 12 pages, 6 figures, 3 tables. This paper is part of the LOFAR surveys data release 1 and has been accepted for publication in a special edition of A&A that will appear in Feb 2019, volume 622. The catalogues and images from the data release will be publicly available on lofar-surveys.org upon publication of the journal

Here we explore the disk-jet connection in the broad-line radio quasar 4C+74.26, utilizing the results of the multiwavelength monitoring of the source. The target is unique in that its radiative output at radio wavelengths is dominated by a moderately-beamed nuclear jet, at optical frequencies by the accretion disk, and in the hard X-ray range by the disk corona. Our analysis reveals a correlation (local and global significance of 96\% and 98\%, respectively) between the optical and radio bands, with the disk lagging behind the jet by $250 \pm 42$ days. We discuss the possible explanation for this, speculating that the observed disk and the jet flux changes are generated by magnetic fluctuations originating within the innermost parts of a truncated disk, and that the lag is related to a delayed radiative response of the disk when compared with the propagation timescale of magnetic perturbations along relativistic outflow. This scenario is supported by the re-analysis of the NuSTAR data, modelled in terms of a relativistic reflection from the disk illuminated by the coronal emission, which returns the inner disk radius $R_{\rm in}/R_{\rm ISCO} =35^{+40}_{-16}$. We discuss the global energetics in the system, arguing that while the accretion proceeds at the Eddington rate, with the accretion-related bolometric luminosity $L_{\rm bol} \sim 9 \times 10^{46}$ erg s$^{-1}$ $\sim 0.2 L_{\rm Edd}$, the jet total kinetic energy $L_\textrm{j} \sim 4 \times 10^{44}$ erg s$^{-1}$, inferred from the dynamical modelling of the giant radio lobes in the source, constitutes only a small fraction of the available accretion power., Comment: 9 pages and 6 figures, ApJ accepted

In this paper, we test the possibility that the structure of the largest radio galaxy J1420-0545 may have been formed by restarted rather than primary jet activity. This hypothesis was motivated by the unusual morphological properties of the source consisting of two edge-brightened, narrow, highly collinear, and symmetric lobes, thus suggesting an almost ballistic propagation of powerful jets into a particularly low-density external medium. New observations made with the VLA together with the currently available GLEAM and TGSS ADR1 data releases allow the detection of an excess emission at low frequencies. An extracted part (88 MHz - 200 MHz) of the spectrum of the emission is fitted with the DYNAGE model, giving a forecast for the environmental conditions and the energetic requirements for the presumed old cocoon related to a preceding epoch of jet activity., Comment: 8 pages, 3 figures, 3 tables

We report the outcome of multifrequency radio observations of a double-double radio source J1706+4340 carried out with the Very Large Array and Giant Metrewave Radio Telescope. After supplementing our own data with those available in the literature, we collected a considerable set of radio measurements covering the range from 74 to 8460 MHz. This has enabled us to perform a comprehensive review of physical properties of the source and its dynamical evolution analysis. In particular, we found that, while the age of the large-scale outer lobes is in the range 260-300 Myr, the renewal of the jet activity, which is directly responsible for the double-double structure, took place only about 12 Myr ago after about 27-Myr long period of quiescence. Another important property of J1706+4340 we found is that the injection spectral indices and the jet powers for the inner and the outer doubles are very similar. This implies that it is the spin of the supermassive black hole rather than e.g. an instability of the accretion disc that is likely responsible for the jet production and its properties., Comment: 11 pages, 4 figures, accepted for publication in MNRAS

Radio galaxies classified as X-shaped/winged, are characterised by two pairs of extended and misaligned lobes, which suggest a rapid realignment of the jet axis, for which a potential cause is still under debate. Here we analyse the complex radio structure of 3C 293 winged source hosted by the post-merger galaxy, which uniquely displays a significant asymmetry between the sizes of the two pairs of lobes, indicating that an episode of jet realignment took place only very recently. Based on all the available radio data for 3C 293, we have performed a detailed spectral modelling for the older and younger lobes in the system. In this way we derived the lobes' ages and jet energetics, which we then compared to the accretion power in the source. We found that the 200 kpc-scale outer lobes of 3C 293 are ~60 Myr old and that jet activity related to the formation of the outer lobes ceased within the last Myr. Meanwhile, the inner 4 kpc-scale lobes, tilted by ~40 deg with respect to the outer ones, are only about ~0.3 Myr old. The best model fits also return identical values of the jet power supplying the outer and the inner structures. This power is of the order of the maximum kinetic luminosity of a Blandford-Znajek jet for a given black hole mass and accretion rate, but only in the case of relatively low values of a black hole spin, a~0.2. The derived jet energetics and timescales, along with the presence of two optical nuclei in 3C 293, all provide a strong support to the Lense-Thirring precession model in which the supermassive black hole spin, and therefore the jet axis, flips rapidly owing to the interactions with the tilted accretion disk in a new tidal interaction episode of the merging process. We further speculate that, in general, X-shape radio morphology forms in post-merger systems that are rich in cold molecular gas, and only host slowly spinning supermassive black holes., Comment: Astronomy & Astrophysics, in press

Relativistic and magnetised plasma ejected by radio loud AGNs through jets form the diffuse lobes of radio galaxies. The radiating particles (electron/electron-positron) in lobes emit in radio via the synchrotron process and X-ray via inverse-Compton scattering of cosmic microwave background photons. The thermal environment around radio galaxies emits X-rays via the thermal bremsstrahlung process. By combining information from these processes we can measure physical conditions in and around the radio lobes and thus study the dynamics of radio galaxies, including double-double radio galaxies., Comment: 11 pages, 4 figures, Diffuse Radio Plasma Conference proceedings (held in Raman Research Institute, Bangalore, India)

In this paper we consider the possibility that the structure of the largest radio galaxy J1420-0545 is formed by a restarted rather than a primary jet activity. This hypothesis is motivated by the unusual morphological properties of the source, suggesting almost ballistic propagation of powerful jets in a particularly low-density environment. New radio observations of J1420-0545 confirm its morphology consisting of only two narrow lobes; no trace of any outer low-density cavity due to the previous jet activity is therefore detected. Different model fits performed using the newly accessed radio data imply relatively young age of the source, its exceptionally high expansion velocity, large jet kinetic power, and confirm particularly low-density environment. We find that it is possible to choose a realistic set of the model parameters for which the hypothetical outer lobes of J1420-0545 are old enough so that their expected radio surface brightness is substantially below the rms noise level of the available radio maps. On the other hand, the extremely low density of the gas surrounding the J1420-0545 lobes is consistent with the mean density of the baryonic matter in the Universe. This suggests that the source may be instead located in a real void of the galaxy and matter distribution. In both cases the giant radio lobes of J1420-0545 are expected to modify substantially the surrounding matter by driving strong shocks and heating the gas located at the outskirts of the filamentary galactic distribution. Finally, we also find that the energetic requirements for the source are severe in terms of the total jet power and the total energy deposited by the outflows far away from the central engine., Comment: 42 pages, 9 figures, 6 tables; Accepted for publication in ApJ

hree limited samples of high-redshift radio sources of FRII-type are used to constrain the dynamical model for the jets' propagation through the two-media environment: the X-ray emitting halo with the power-law density profile surrounding the parent galaxy and the much hotter intergalactic medium (IGM) of a constant density. The model originally developed by Gopal-Krishna & Wiita (1987) is modified adopting modern values of its free parameters taken from recent X-ray measurements with the XMM-Newton and Chandra Observatories. We find that (i) giant-sized radio sources ($\sim$1 Mpc) exist at redshifts up to $z\sim 2$, (ii) all newly identified the largest radio sources with $1

Using the new low-frequency and high-frequency radio images of this galaxy, we determined the shape of the spectrum along its lobes and performed the classical spectral-ageing analysis. On the other hand, we applied the analytical model of the jet's dynamics, which allowed us to derive the physical conditions for the source's evolution during the original jet propagation through the unperturbed IGM, as well as those when the restarted new jet propagates inside the outer cocoon formed by the old jet material that passed through the jet terminal shock. The dynamical age estimate of the outer and the inner lobes is 132+/-28 Myr and ~9+/-4 Myr, respectively. The synchrotron age in the outer lobes systematically rises from ~25 Myr in the vicinity of the lobes' edges to about 65-75 Myr in the centre of the old cocoon. These ages imply an average expansion speed along the jets' axis: (0.012+/-0.003)c in the outer lobes and (0.058+/-0.025)c in the inner lobes, but the latter speed would be ~0.25c when they were of age less than 1 Myr. We find that the jet power during the restarted activity is about ten-fold fainter than that of the original jet. Similar disproportion is found for the internal pressures and the magnetic field strengths in the old cocoon and those in the inner lobes. This disproportion can be effectively reduced by assuming the same equations of state for the emitting particles and the magnetic fields within the old and the new lobes. However, we think that our assumption of the non-relativistic equation of state for the old cocoon and the relativistic one for the new lobes is more justified., Comment: Accepted for publication in Astronomy and Astrophysics, 18 pages, 10 figures

Dynamical ages of the opposite lobes determined {\sl independently} of each other suggest that their ratios are between $\sim$1.1 to $\sim$1.4. Demanding similar values of the jet power and the radio core density for the same GRS, we look for a {\sl self-consistent} solution for the opposite lobes, which results in different density profiles along them found by the fit. A comparison of the dynamical and spectral ages shows that their ratio is between $\sim$1 and $\sim$5, i.e. is similar to that found for smaller radio galaxies. Two causes of this effect are pointed out., Comment: To appear in ASP Conference Series, Vol. 407, The Low-Frequency Radio Universe, eds D. J. Saikia, D. A. Green, Y. Gupta and T. Venturi (Conference held at NCRA, Pune, India from 8th to 12th December 2008)

Multifrequency observations with the GMRT and the VLA are used to determine the spectral breaks in consecutive strips along the lobes of a sample of selected giant radio sources (GRSs) in order to estimate their spectral ages. The maximum spectral ages estimated for the detected radio emission in the lobes of our sample of ten sources has a median value of $\sim$20 Myr. The spectral ages of these GRSs are significantly older than smaller sources. In all but one source (J1313+6937) the spectral age gradually increases with distance from the hotspot regions, confirming that acceleration of the particles mainly occurs in the hotspots. Most of the GRSs do not exhibit zero spectral ages in the hotspots. This is likely to be largely due to contamination by more extended emission due to relatively modest resolutions. The injection spectral indices range from $\sim$0.55 to 0.88 with a median value of $\sim$0.6. We show that the injection spectral index appears to be correlated with luminosity and/or redshift as well as with linear size., Comment: To appear in ASP Conference Series, Vol. 407, The Low-Frequency Radio Universe, eds D. J. Saikia, D. A. Green, Y. Gupta and T. Venturi (Conference held at NCRA, Pune, India from 8th to 12th December 2008)

One of the striking examples of episodic activity in active galactic nuclei are the double-double radio galaxies (DDRGs) with two pairs of oppositely-directed radio lobes from two different cycles of activity. We illustrate, using the DDRG J1453+3308 as an example, that observations over a wide range of frequencies using both the GMRT and the VLA can be used to determine the spectra of the inner and outer lobes, estimate their spectral ages, estimate the time scales of episodic activity, and examine any difference in the injection spectra in the two cycles of activity. Low-frequency GMRT observations also suggest that DDRGs and triple-double radio galaxies are rather rare., Comment: To appear in ASP Conference Series, Vol. 407, The Low-Frequency Radio Universe, eds D. J. Saikia, D. A. Green, Y. Gupta and T. Venturi (Conference held at NCRA, Pune, India from 8th to 12th December 2008)

The dynamical ages of the opposite lobes of selected giant radio sources are estimated using the DYNAGE algorithm of Machalski et al., and compared with their spectral ages estimated and studied by Jamrozy et al. in Paper II. As expected, the DYNAGE fits give slightly different dynamical ages and other model's parameters for the opposite lobes modelled independently each other, e.g. the age ratios are found between ~1.1 to ~1.4. Demanding similar values of the jet power and the radio core density for the same source, we look for a self-consistent solution for the opposite lobes, which results in different density profiles along them found by the fit. We also show that a departure from the equipartition conditions assumed in the model, justified by X-ray observations of the lobes of some nearby radio galaxies, and a relevant variation of the magnetic-field strengths may provide an equalisation of the lobes' ages. A comparison of the dynamical and spectral ages shows that a ratio of the dynamical age to the spectral age of the lobes of investigated giant radio galaxies is between ~1 and ~5, i.e. is similar to that found for smaller radio galaxies (e.g. Parma et al. 1999). Supplementing possible causes for this effect already discussed in the literature, like uncertainty of assumed parameters of the model, an influence of a possible departure from the energy equipartition assumption, etc. Arguments are given to suggest that DYNAGE can better take account of radiative effects at lower frequencies than the spectral-ageing analysis.The DYNAGE algorithm is especially effective for sources at high redshifts, for which an intrinsic spectral curvature is shifted to low frequencies., Comment: Accepted to MNRAS, 12 pages, 6 figures, 4 tables

We report the discovery of the largest giant radio galaxy, J1420-0545: a FR type II radio source with an angular size of 17.4' identified with an optical galaxy at z=0.3067. Thus, the projected linear size of the radio structure is 4.69 Mpc (if we assume that H_{0}=71 km\s\Mpc, Omega_{m}=0.27, and Omega_{\Lambda}=0.73). This makes it larger than 3C236, which is the largest double radio source known to date. New radio observations with the 100 m Effelsberg telescope and the Giant Metrewave Radio Telescope, as well as optical identification with a host galaxy and its optical spectroscopy with the William Herschel Telescope are reported. The spectrum of J1420-0545 is typical of elliptical galaxies in which continuum emission with the characteristic 4000A discontinuity and the H and K absorption lines are dominated by evolved stars. The dynamical age of the source, its jets' power, the energy density, and the equipartition magnetic field are calculated and compared with the corresponding parameters of other giant and normal-sized radio galaxies from a comparison sample. The source is characterized by the exceptionally low density of the surrounding IGM and an unexpectedly high expansion speed of the source along the jet axis. All of these may suggest a large inhomogeneity of the IGM., Comment: 20 pages, 5 figures, 3 tables

Multifrequency observations with the GMRT and the VLA are used to determine the spectral breaks in consecutive strips along the lobes of a sample of selected giant radio sources (GRSs) in order to estimate their spectral ages. The maximum spectral ages estimated for the detected radio emission in the lobes of our sources range from $\sim$6 to 36 Myr with a median value of $\sim$20 Myr using the classical equipartition fields. Using the magnetic field estimates from the Beck & Krause formalism the spectral ages range from $\sim$5 to 38 Myr with a median value of $\sim$22 Myr. These ages are significantly older than smaller sources. In all but one source (J1313+6937) the spectral age gradually increases with distance from the hotspot regions, confirming that acceleration of the particles mainly occurs in the hotspots. Most of the GRSs do not exhibit zero spectral ages in the hotspots, as is the case in earlier studies of smaller sources. This is likely to be largely due to contamination by more extended emission due to relatively modest resolutions. The injection spectral indices range from $\sim$0.55 to 0.88 with a median value of $\sim$0.6. We discuss these values in the light of theoretical expectations, and show that the injection spectral index appears to be correlated with luminosity and/or redshift as well as with linear size., Comment: 12 Pages, 13 Figures, 9 Tables, Accepted for publication in MNRAS

A problem of the cosmological evolution of the IGM is recalled and a necessity to find distant (z>0.5) giant radio galaxies (GRGs) with the lobe energy densities lower than about 10^{-14} J m^{-3} to solve this problem is emphasized. Therefore we undertake a search for such GRGs on the southern sky hemisphere using the SALT. In this paper we present a selected sample of the GRG candidates and the first deep detections of distant host galaxies, as well as the low-resolution spectra of the galaxies identified on the DSS frames. The data collected during the Performance Verification (P-V) phase show that 21 of 35 galaxies with the spectroscopic redshift have the projected linear size greater than 1 Mpc (for H_{0}=71 km\s\Mpc). However their redshifts do not exceed the value of 0.4 and the energy density in only two of them is less than 10^{-14} J m^{-3}. A photometric redshift estimate of one of them (J1420-0545) suggests a linear extent larger than 4.8 Mpc, i.e. a larger than that of 3C236, the largest GRG known up to now., Comment: 22 pages, 17 Postscript figures, 6 tables

We present low-frequency observations with the Giant Metrewave Radio Telescope (GMRT) of a sample of giant radio sources (GRSs), and high-frequency observations of three of these sources with the Very Large Array (VLA). From multifrequency observations of the lobes we estimate the magnetic field strengths using three different approaches, and show that these differ at most by a factor of $\sim$3. For these large radio sources the inverse-Compton losses usually dominate over synchrotron losses when estimates of the classical minimum energy magnetic field are used, consistent with earlier studies. However, this is often not true if the magnetic fields are close to the values estimated using the formalism of Beck & Krause. We also examine the spectral indices of the cores and any evidence of recurrent activity in these sources. We probe the environment using the symmetry parameters of these sources and suggest that their environments are often asymmetric on scales of $\sim$1 Mpc, consistent with earlier studies., Comment: 14 pages, 5 figures, 6 tables, one appendix; accepted for publication in MNRAS

We propose a new approach in determining ages of FR II type radio sources. We apply the assumed dynamical model of Kaiser et al. (1997) to a number of FR II type radio galaxies observed at different radio frequencies, and fit - for each frequency separately - the model free parameters to the observed sources' quantities. Such a procedure, using enlarged in fact a number of observables, enables us to determine relatively precise ages and other crucial characteristics of the analyzed sources. The resulting age estimates agree very well with those obtained by means of `classical' spectral ageing method for objects not older than 10 Myr, for which good-quality spectral data are available. The presented method is however also applicable in the case of the sources older than this, and/or the ones for which the only available low-resolution radio data do not allow for detailed spectral ageing studies. Our analysis indicates that the main factor precluding precise age determination for FR II type radio galaxies regards the poorly known shape of the initial electron energy distribution injected by the jet terminal shocks to the expanding lobes/cocoons. We briefly consider this issue, and conclude that the broad-band single power-law form assumed here may be accurate enough for the presented estimates, although most likely it does not strictly correspond to some well-defined realistic particle acceleration process. Instead, it should be considered as a simplest model approximation of the initial electron continuum, averaged over a very broad energy range and over the age of the source, with the effective spectral index which may be different for different sources., Comment: 15 pages, 9 figures included. Accepted for publication in A&A

We present new radio observations at frequencies ranging from 240 to 4860 MHz of the well-known, double-double radio galaxy (DDRG), J1453+3308, using both the Giant Metrewave Radio Telescope (GMRT) and the Very Large Array (VLA). These observations enable us to determine the spectra of the inner and outer lobes over a large frequency range and demonstrate that while the spectrum of the outer lobes exhibits significant curvature, that of the inner lobes appears practically straight. The break frequency, and hence the inferred synchrotron age of the outer structure, determined from 16$-$arcsec strips transverse to the source axis, increases with distance from the heads of the lobes. The maximum spectral ages for the northern and southern lobes are $\sim$47 and 58 Myr respectively. Because of the difference in the lengths of the lobes these ages imply a mean separation velocity of the heads of the lobes from the emitting plasma of 0.036c for both the northern and southern lobes. The synchrotron age of the inner double is about 2 Myr which implies an advance velocity of $\sim$0.1c, but these values have large uncertainties because the spectrum is practically straight., Comment: 10 pages, 10 figures, 5 tables, accepted for publication in MNRAS

In this paper we analyse whether `giant' radio galaxies (GRGs) differ from `normal'-size galaxies (NSGs) except for the linear extent of their radio structure. We compare a number of properties of GRGs with the corresponding properties of NSGs, and analyse the statistical trends and correlations of physical parameters, homogeneously determined for the sources, with their `fundamental' parameters. Using the Pearson partial-correlation test on the correlation between two variables in the presence of one or two other variables, we examine which correlation is the strongest. The analysis clearly shows that GRGs do not form a separate class of radio sources. They most likely evolve with time from smaller sources, however under specific circumstances. Analysing properties of GRGs and NSGs together, we find that (i) the core prominence does not correlate with the total radio luminosity (as does the core power), but it anti-correlates with the surface brightness of the lobes of sources, (ii) the energy density (and possibly the internal pressure) in the lobes is independent of redshift for constant radio luminosity and size of the sources, (iii) the equipartition magnetic-field strength, transformed into constant source luminosity and redshift, strongly correlates with the source size. We argue that this B_{eq} - D correlation reflects a more fundamental correlation between B_{eq} and the source age, (iv) both the rotation and depolarisation measures suggest Faraday screens local to the lobes of sources, however their geometry and the composition of intervening material cannot be determined from the global polarisation characteristics., Comment: 10 pages, 8 figures, 6 tables. Accepted for publication in A&A

Our sample of giant radio-source candidates, published in Paper I (Machalski et al. 2001), is updated and supplemented with further radio and optical data. In this paper we present: (i) newly detected host galaxies, their photometric magnitude, and redshift estimate for the sample sources not identified yet, (ii) optical spectra and spectroscopic redshift for the host galaxies fainter than about 18.5 mag taken with the Apache Point Observatory 3.5m telescope, and (iii) the VLA 4.9 GHz total-intensity and polarised-intensity radio maps of the sample members. In a few cases they reveal extremely faint radio cores undetected before, which confirm the previously uncertain optical identifications. The radio maps are analysed and the polarisation properties of the sample sources summarised. A comparison of our updated sample with three samples published by other authors implies that all these four samples probe the same part of the population of extragalactic radio sources. There is no significant difference between the distributions of intrinsic size and radio power among these samples. The median redshift of 0.38 +/- 0.07 in our sample is the highest among the corresponding values in the four samples, indicating that the angular size and flux-density limits in our sample, lower than those for the other three samples, result in effective detections of more distant, giant-size galaxies compared to those detected in the other samples. This sample and a comparison sample of `normal'-size radio galaxies will be used in Paper III (Machalski & Jamrozy 2006) to investigate of a number of trends and correlations in the entire data., Comment: 30 pages, 21 figures, 6 tables. Accepted for publication in A&A. Version with high resolution figures available from http://www.oa.uj.edu.pl/~jamrozy/

The time evolution of giant lobe-dominated radio galaxies (with projected linear size D>1 Mpc if H_{0}=50 km/s/Mpc and q_{0}=0.5 is analysed on the basis of dynamical evolution of the entire FRII-type population. Two basic physical parameters, namely the jet power Q_{0} and central density of the galaxy nucleus rho0 are derived for a sample of giants with synchrotron ages reliably determined, and compared with the relevant parameters in a comparison sample of normal-size sources consisting of 3C, B2, and other sources. Having the apparent radio luminosity P and linear size D of each sample source, Q_{0} and rho_{0} are obtained by fitting the dynamical model of Kaiser et al. (1997). We find that: (i) there is not a unique factor governing the source size; they are old sources with temperate jet power (Q_{0}) evolved in a relatively low-density environment (rho_{0}). The size is dependent, in order of decreasing partial correlation coefficients, on age; then on Q_{0}; next on rho_{0}. (ii) A self-similar expansion of the sources' cocoon seems to be feasible if the power supplied by the jets is a few orders of magnitude above the minimum-energy value. In other cases the expansion can only initially be self-similar; a departure from self-similarity for large and old sources is justified by observational data of giant sources. (iii) An apparent increase of the lowest internal pressure value observed within the largest sources' cocoon with redshift is obscured by the intrinsic dependence of their size on age and the age on redshift, which hinders us from making definite conclusions about a cosmological evolution of intergalactic medium (IGM) pressure., Comment: 36 pages, 8 figures, 7 tables

The time evolution of `fiducial' radio sources derived from fitting the dynamical model of Kaiser et al. (1997) is compared with the observational data for the `clan' sources found in the sample of giant and normal-size FRII-type sources published Paper I (Machalski et al. 2004). Each `clan' comprises 3, 4 or 5 sample sources having similar values of the two basic physical parameters: the jet power Q_{0} and central density of the galaxy nucleus rho_{0} (determined in Paper I) but different ages, radio luminosities and axial ratios. These sources are considered as the `same' source observed at different epochs of its lifetime and used to fit the evolutionary luminosity-size (P-D) and energy density-total energy (u_{c}-E_{tot}) tracks derived from the model for a `fiducial' source with Q0 and rho_{0} equal to the means of relevant values obtained for the `clan' members, as well as to constrain the evolutionary model of the source dynamics used. In the result we find that (i) The best fit is achieved when the Kaiser et al.'s model is modified by allowing an evolution of the sources' cocoon axial ratio with time as suggested by Blundell et al. (1999). (ii) A slow acceleration of the average expansion speed of the cocoon along the jet axis is suggested by the `clan' sources. We argue that this acceleration, although minor, may be real and some supporting arguments come from the well known hydrodynamical considerations., Comment: 14 pages, 4 figures, 1 tables, Acta Astronomica in press

Giant radio galaxies (GRGs), with linear sizes larger than 1 Mpc (H0=50 km/s/Mpc), represent the biggest single objects in the Universe. GRGs are rare among the entire population of radio galaxies (RGs) and their physical evolution is not well understood though for many years they have been of special interest for several reasons. The lobes of radio sources can compress cold gas clumps and trigger star or even dwarf galaxy formation, they can also transport gas from a host galaxy to large distances and seed the IGM with magnetic fields. Since GRGs have about 10 to 100 times larger sizes than normal RGs, their influence on the ambient medium is correspondingly wider and is pronounced on scales comparable to those of clusters of galaxies or larger. Therefore `giants' could play an important role in the process of large-scale structure formation in the Universe. Recently, thanks to the new all sky radio surveys, significant progress in searching for new GRGs has been made., Comment: To appear in Multiwavelength AGN Surveys, ed. R. Maiolino and R. Mujica, Singapore: World Scientific, 2004, 2 pages

An extensive search for distant Giant radio galaxies on the southern hemisphere is justified. We emphasize the crucial role of optical spectroscopy in determination of their basic physical parameters, i.e. the distance, projected linear size, volume of their lobes or cocoon, luminosity, etc., and argue that SALT will be the best instrument for such a task., Comment: 4 pages, 5 Postscript figures, uses newpasp.sty, to be published in " Science with SALT"

Very deep 4.9 GHz observations with the VLA are used to supplement available radio maps at the frequencies of 325 MHz (WENSS survey) and 1.4 GHz (NVSS survey) in order to study the synchrotron spectra and radiative ages of relativistic particles in the extended lobes of distant giant radio galaxies selected from the sample of Machalski et al. (2001)., Comment: 4 pages, 4 Postscript figures, uses baltlat1.sty; To be published in "Radio astronomy at 70: from Karl Jansky to microjansky", JENAM-2003 Symposium, eds. L.Gurvits and S.Frey, (Baltic Astronomy)

The time evolution of giant (D>1 Mpc) lobe-dominated galaxies is analysed on the basis of dynamical evolution of the entire FRII-type population., Comment: 4 pages, 2 Postscript figures, uses baltlat1.sty To be published in "Radio astronomy at 70: from Karl Jansky to microjansky", JENAM-2003 Symposium, eds. L.Gurvits and S.Frey, (Baltic Astronomy)

The redshifts of faint radio galaxies identified with giant radio source candidates selected from the sample of Machalski et al. (2001) have been measured. Given the redshift, the projected linear size and radio luminosity are then determined. The above, supplemented with the axial ratio of the sources (evaluated from the radio maps) allows to constrain their jet power and the dynamical age using the analytical model of Kaiser et al. (1997) but modified by allowing the axial ratio of the source's cocoon to evolve in time., Comment: 4 pages, 3 Postscript figures, uses baltlat1.sty To be published in "Radio astronomy at 70: from Karl Jansky to microjansky", JENAM-2003 Symposium, eds. L.Gurvits and S.Frey, (Baltic Astronomy)

A time evolution of giant lobe-dominated radio galaxies (with projected linear size $D>1$ Mpc) is analysed on the basis of dynamical evolution of the entire FRII-type population. Two basic physical parameters, namely the jet power $Q_{0}$ and central density of the galaxy nucleus $\rho_{0}$ are derived for a sample of giants with synchrotron ages reliably determined, and compared with the relevant parameters in a comparison sample of normal-size sources consisting of 3C, B2, and other sources. Having apparent luminosity (power) $P$ and linear size $D$ of each sample source, $Q_{0}$ and $\rho_{0}$ are fitted using the dynamical model of Kaiser et al. (1997) but modified by allowing an evolution of the cocoon axial ratio with time as suggested by Blundell et al. (1999). In a result, we found that: (i) there is not a unique factor governing the source size; giants are old sources with high enough jet power evolved in a relatively low-density environment. The size is dependent, in order of decreasing partial correlation coefficients, on age; then on $Q_{0}$; next on $\rho_{0}$, (ii) a number of the sample sources, having similar $Q_{0}$ and $\rho_{0}$ but different ages and axial ratios (called a `clan'), fit very well the evolutionary luminosity-size ($P$-$D$) and energy density-total energy tracks derived from the model for a `fiducial' source with $Q_{0}$ and $\rho_{0}$ equal to the means of relevant values obtained for the `clan' members. Therefore, these sources can be considered as `the same' source observed at different epochs of its lifetime, and hence very useful for an observational constraint of evolutionary models of the source dynamics, (iii) in some cases a slow acceleration of the average expansion speed of the cocoon along the jet axis seems to be present., Comment: 27 pages, 9 figures, gzipped ps-file of the manuscript also available at http://www.oa.uj.edu.pl/~chris/giants.ps.gz

A new sample of very large angular size radio sources has been selected from the 1.4 GHz VLA surveys: FIRST and NVSS. This sample will be very useful for an observational constraint on the time evolution of double radio sources, especially their size, predicted by numerous analytical models of such evolution (cf. Introduction). In this paper we present radio and optical data for a large fraction of the sample sources. They are: high-frequency VLA maps with very weak radio cores detected, deep optical images showing the identified faint host galaxies not visible on the DSS images, and optical spectra of the identified galaxies brighter than about R ~ 18.5 mag taken with the McDonald Observatory 2.1m telescope. For 15 galaxies (of which 4 do not belong to the complete sample) the redshift has been determined. In the result, 44 per cent of galaxies in the complete sample have redshift data (with one exception all redshifts are less than 0.33), of which 70 per cent have a linear size exceeding 1 Mpc. The photometric redshift estimates for other 11 galaxies with 19 mag

A radio source of the Fanaroff--Riley type II with the angular size of 11.3 arc min is identified with an optical galaxy at z=0.229. Thus, the projected linear extent of the radio structure is 3.14 Mpc which makes it the third largest classical double radio source known after 3C236 and WNB2147+816. The high-frequency VLA observations, a galaxy identification and its optical spectroscopy are reported. The equipartition magnetic field and energy density in the source is calculated and compared with corresponding parameters of other giants known, indicating that either parameter of the source investigated is extremely low. On the other hand, the age estimate of relativistic electrons and the advance speed of the lobe material are comparable to the respective parameters characterizing other low-luminosity giant sources, as well as much smaller and brighter 3CR sources. The environment analysis suggests that J1343+3758 lies in a significantly poor region of intergalactic medium., Comment: 4 pages, 4 figures, accepted for publication in A&A Letters A higher resolution version of the paper is available at http://www.oa.uj.edu.pl/~jamrozy

The evidence are given that the radio source GB2 0909+353 (GB2 catalogue: Machalski 1978; ICRS 2000.0 coordinates: 09 12 51.7, +35 10 10) is likely one of the largest classical doubles known, though its optical identification is not certain. Our deep VLA observations at 5 GHz did not reveal a radio core brighter than 0.5 mJy/beam at this frequency. Thus a distance to the source is evaluated using photometric -- redshift estimates of the faint galaxies in the optical field. The equipartition magnetic field and energy density in the source is calculated and compared with corresponding parameters of other `giant' radio sources known, showing extremely low values of both physical parameters of the source investigated. On the other hand, the age of relativistic electrons, and the advance speed of the `hot spot' in the source are typical for much smaller and brighter 3CR sources., Comment: 10 pages with 3 Postscript figures, accepted to Acta Astronomica

A preliminary 1.4 GHz RLF at redshift of about 0.14 is derived from the Las Campanas Redshift Survey (LCRS) and the NVSS radio data. No significant evolution has been found at this redshift in comparison to the 'local' RLF., Comment: 2 pages including 2 Postscript figures, uses crckapb10.sty

It is shown that the new observed redshift distributions of various flux-limited samples of radio sources in general are consistent with the predictions of two basic evolutionary models published by Condon (1984) and Dunlop and Peacock (1990), i.e. none of them can be rejected at the confidence level of about 95 per cent. However, the models allowing a free-form evolution and suggesting both density and luminosity evolution are more consistent with the observational data at lower redshifts, while the 'pure luminosity evolution' model fits better the data at higher redshifts. This leads to a suspicion that the same evolution governing all radio sources, suggested by Condon (1984), might not be the case., Comment: 4 pages including 2 Postscript figures, uses crckapb10.sty