Components Of Radio Sources Research Articles

WSRT observations of core-dominated radio sources

A few years ago we presented evidence for large scale radio structures around most superluminal radio sources (Schilizzi and de Bruyn, 1983). The extended emission is relatively faint and, in at least two cases (3C120 and 30345), exhibits a rather complex morphology. Although the sample was small, the conclusion seemed inescapable that the largest angular sizes (LAS) of the superluminals do not permit a large deprojection factor due to foreshortening, without making these sources exceptionally large intrinsically. That is to say, they would be exceptional within the context of the unified scheme (US) which interprets superluminal sources as favourably oriented, strongly beamed, core components of classical double radio sources. To save the US, we concluded that the ejection axes of these sources must undergo a large (≥ 30°) change of direction in the period between the creation of the outer and inner emission regions. Superluminality would then be a temporary phase (although possibly recurrent) in the lifespan of a large fraction of the parent population of classical doubles.

The angular dimensions of extragalactic radio sources

The angular dimensions of compact components of extragalactic radio sources are calculated theoretically on three hypotheses: (a) magnetic field and relativistic particles energy equipartition; (b) equilibrium between synchrotron and Compton losses; (c) radiative lifetime of the same order as the source's light-travel time. Using angular measurements of 73 radio components, divided into two groups (multicomponent and single-component sources), a correcting formulae is derived to reduce the theoretical values to the observed values.

Radio Galaxies and Quasars in Clusters of Galaxies

The study of radio galaxies situated within clusters of galaxies has become a broad field, with hundreds of papers published in the last few years. This review will therefore be restricted mainly to consideration of the interactions between the extended components of radio sources in clusters and the diffuse gas (intracluster medium, ICM) which occurs in clusters. In particular, attention will be focused on what we can learn about the ICM from this interaction, in conjunction with other data such as X-ray observations. In the case of quasars in clusters of galaxies the emphasis is rather different, so discussion of this topic is deferred to section 6.

Optical Inverse Compton Emission in Extragalactic Radio Sources

In this contribution the reported detection by Saslaw, Tyson and Crane (1978) of weak optical emission in the lobes of three 3C sources — 3C 265, 3C 285 and 3C 390.3 — is reappraised in the framework of three optical emission mechanisms — synchrotron (SYN), synchrotron inverse Compton (SIC) and blackbody inverse Compton (BIC). This effort has been motivated partly by the knowledge that the contribution to the synchrotron inverse Compton emission in a radio source component is likely to become significant for very compact and bright radio components (see e.g. Okoye 1972), and partly by the recent availability of high resolution radio frequency structural data on the sources in question. Another incentive arose from the demands of a separate investigation into high energy particles interactions in radio sources (reported by Okoye and Okeke in this volume) involving very high energy protons thus making it necessary to ascertain whether such highly energetic particles exist in radio source components.

Proton-Proton Collisions in Extragalactic Radio Sources

The majority of extragalactic radio sources are known to consist of two extended components straddling an optical galaxy or quasar with each component being maintained from the nucleus of the associated optical object through a beam or jet of relativistic plasma and magnetic fields. Hitherto, the energetics of radio source components have been considered essentially from the point of view of the cooling of the relativistic electrons through their interaction with ambient magnetic fields (synchrotron radiation) and with low energy photons (inverse Compton emission). Here we consider a hitherto neglected problem involving the mutual interactions between the fast particles themselves. (The results of a detailed investigation into these interactions will be reported elsewhere — see Okoye and Okeke, 1982.)

Effects of gamma-ray, neutrino, and particle production on the energetics and dynamics of compact extragalactic radio sources

Consideration is given to particle production and high-energy radiation within apparently superluminal radio components of extragalactic radio sources forming within the apparent region of nuclear activity of a quasar or active galaxy. The physical conditions in compact components observed as radio emitters are derived for the quasars 3C 273 and 3C 345 and extrapolated to those of initial components of sizes on the order of 10 to the 15th cm on the basis of two-dimensional relativistic jet and relativistic three-dimensional models of component expansion. Probabilities that a given particle avoids an inelastic collision in the relativistic plasma are calculated for both cases which show that collisions which produce particles and radiation may be very important during the formation of a compact radio component. The consequences of electron-positron production, bremsstrahlung and proton-proton inelastic collisions ultimately giving rise to neutrinos and gamma rays for the development and energetics of the radio component are then examined, and upper limits to the amount of energy which can be channeled into radio components from an active region without giving rise to a high-energy X-ray source are derived.

A method of mapping compact structure in radio sources using VLBI observations

A two-part technique is described for determining the angular structure of the compact components of radio sources from VLBI observations. With this technique, the source structure is first approximated, using both amplitudes and closure phases, by a model consisting of circularly symmetric Gaussian components located on a grid of positions on the sky. The second part begins by employing this model to predict the visibility phase corresponding to each observed visibility amplitude; these estimated visibility phases are then adjusted to agree with the observed closure phases. The resulting estimates of the visibility phases and the observed visibility amplitudes are then combined in a direct Fourier transform to produce a 'dirty' source map that is deconvolved via the CLEAN procedure on the basis of the point-source response. Some examples based on data generated from test models are provided.

Image Reconstruction from VLBI Amplitude and Phase Closure Data

AbstractA two step procedure is developed for the determination of the angular structure of the compact components of radio sources from observations made with very long baseline interferometry (VLBI). The first step is to fit a model composed of circularly symmetric Gaussian components to the observations. Then this, or any other, model and closure phase information is used to predict visibility phases which, when paired with the corresponding visibility amplitude observation, are combined in a direct synthesis; the resulting map is deconvolved from the point source response by means of the “CLEAN” procedure. If necessary, the “cleaned” components can be used as a starting model to predict visibility phases and the process iterated. The initial model in many cases may be as simple as a point source. Convergence of this process appears to be quite rapid, requiring only a few iterations when the source is simple or the starting model is good. These two steps for source mapping can be used either together or separately. Examples are given using data generated from test models.

Symmetric structure in the slingshot theory of radio galaxies

view Abstract Citations (3) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Symmetric structure in the slingshot theory of radio galaxies. Valtonen, M. J. Abstract According to the slingshot theory, supermassive objects are ejected from galactic nuclei through an instability of a system of three bodies, and they appear as radio source components on both sides of the galaxy. A major difficulty is often thought to arise from the observed symmetry of radio sources with respect to the central galaxy and the tendency of three-body systems to break up asymmetrically. It is shown that there is actually no difficulty in reconciling the theory with existing observations when allowance is made for the fact that asymmetric radio sources do exist, even though not as commonly as symmetric ones, and that the ejected objects have nonzero radii. Publication: The Astrophysical Journal Pub Date: May 1977 DOI: 10.1086/155196 Bibcode: 1977ApJ...213..648V Keywords: Astrophysics; Extragalactic Radio Sources; Galactic Structure; Radio Galaxies; Supermassive Stars; Astronomical Models; Black Holes (Astronomy); Velocity Distribution; Astrophysics full text sources ADS |

Spectra of Compact and Extended Components of Powerful Extragalactic Radio Sources

Spectra of Compact and Extended Components of Powerful Extragalactic Radio Sources

What Docks the Tails of Radio Source Components?

The components of powerful extragalactic radio sources show a characteristic head–tail structure. If synchrotron losses play a major part in limiting the lengths of the tails, the tails should be longer at low frequencies than at high frequencies. New observations of 3C 172 indicate that such differences are not observed, and this conclusion is consistent with published data on other sources.

Massive Black Holes in Extragalactic Radio Source Components?

Massive Black Holes in Extragalactic Radio Source Components?

Australian Journal of Physics Astrophysical Supplements

The results of surveys made at Parkes of linear polarization at wavelengths of 6, 11, 18 and 21 cm are presented for a total of 1121 small-diameter radio sources or source components

New observations of the angular diameter-redshift relation for radio sources

Measurements of the angular sizes of radio source components in the range 0.1″–1.0″, using the technique of interplanetary scintillation, reveal an absence of small–diameter sources at the largest redshifts. The cosmological implications of this result are discussed.

Super-relativistic phase velocities of radio source components

A sudden injection of relativistic electrons at the centre of an extended dipolar magnetic field could lead to an apparent faster-than-light expansion of two synchrotron emitting regions. Subsequent injections of electrons would produce components which move outwards along the same axis.

Position Solution of Compact Radio Sources Using Long Coherence VLBI

Compact components of several radio sources were observed in the course of VLBI observations at S-band between NASA-JPL Deep Space Stations located in Australia, South Africa and California, U.S.A., during the southern summer of 1971–72. These stations were equipped with H-maser frequency standards over this period so that the fringe frequency could be determined to better than 1 mHz.The internal consistency of the position solution could be assessed for sources observed at least three times. This varied with source declination from ± 0″.1 at a declination of 45° to ± 2″.0 near the equator.The spread in the position solution for P0727-11, a rapid variable at the observing frequency, was also large.Positions obtained for some other sources have been used to assist in the identification of associated optical objects.

Bubble Model of Extragalactic Radio Sources

The components of radio sources are identified with bubbles of relativistic plasma rising through the hot gas which produces the X-ray emission from clusters of galaxies. Continuous release of energy in the nucleus of a galaxy will lead to the formation of two such bubbles, moving in opposite directions along the axis of rotation.

The Velocity of Separation of the Components of Extragalactic Radio Sources

Observations of a statistically complete sample of radio sources are used to derive limits to the velocity of separation of the components of typical double radio sources. For the most probable rate of luminosity evolution, the components of a typical source are unlikely to be moving away from the parent galaxy with a velocity exceeding 0.08 c.

Observations of the Structure of Radio Sources in the 3C Catalogue--IV. Correlation Diagrams and the Evolution of Radio Sources

The radio structures of a complete sample of 200 radio sources from the Revised 3C catalogue are now available with a resolution of |${23}^{\prime{}\prime}\,\times\,{23}^{\prime{}\prime}\,\text{cosec}\,\delta$| from recent observations at 1407 MHz with the One-Mile telescope at Cambridge. These results are taken together with other data from long baseline interferometry and studies of interplanetary scintillation to derive correlation diagrams of radio luminosity against surface brightness and of radio luminosity against total linear size at 178 MHz and 1407 MHz. Particular attention is given to the proper selection of sources at different frequencies and the selection effects which can influence the correlation diagrams. It is shown that these correlation diagrams are well determined from the present data. Since the diagrams represent a complete sample of sources it is possible to make quantitative comparison between theories of the evolution of radio sources and the observations. A general procedure has been developed for testing theories in which the components of radio sources are ejected from the nuclei of radio galaxies and QSO's. In this analysis it is essential to incorporate the effects of cosmological evolution, which can considerably change the appearance of the predicted diagrams. It is shown that it is possible to account for a large part of the dispersion in the correlation diagrams as being due to the fact that sources are observed at different stages in their evolution.

A Possible Method for Investigating the Evolution of Radio Galaxies

A method is suggested for determining the velocity of ejection and the ages of the components of double radio sources. The derived variation of the radio luminosity with time suggests that nearly all extra-galactic radio sources, including the most compact quasistellar sources and the most extensive double radio galaxies, can be accounted for by a single model in which clouds of relativistic particles are ejected from the parent galaxy with an initial velocity close to c . This type of variation of radio luminosity with time may be derived independently from the luminosity distribution of radio galaxies. The cloud velocity and the radio luminosity both decrease to a small value after ∼ 3 × 10 6 years. The decrease of luminosity exhibits two main phases, and suggests that all classes of powerful source originate with the release of energetic particles having a total energy of ∼ 10 62 erg, in a galaxy containing a weak magnetic field (≼ 10 −5 gauss). The expansion from an extremely compact object exhibiting the effects of low-frequency self-absorption, must be accompanied by amplification of the magnetic field at the expense of the particle energy, and equipartition may be attained after ∼ 2 × 10 5 years, when the physical separation of the components is approximately equal to the diameter of the galaxy. The subsequent development, corresponding to the most extensive double sources, involves a rapid decrease of radio luminosity with age as the expansion proceeds without field amplification.