We present parametrized broad-band spectral models valid at frequencies between 30 and 300 MHz for six bright radio sources selected from the 3C survey, spread in right ascension from 0 to 24 h. For each source, data from the literature are compiled and tied to a common flux density scale. These data are then used to parametrize an analytic polynomial spectral calibration model. The optimal polynomial order in each case is determined using the ratio of the Bayesian evidence for the candidate models. Maximum likelihood parameter values for each model are presented, with associated errors, and the percentage error in each model as a function of frequency is derived. These spectral models are intended as an initial reference for science from the new generation of low-frequency telescopes now coming online, with particular emphasis on the Low Frequency Array (LOFAR).

/pdf/a-broad-band-flux-scale-for-low-frequency-radio-telescopes-2cjsw0cso2.pdf

A broad-band flux scale for low-frequency radio telescopes

THE radio emission from most strong extragalactic sources is concentrated in a band which passes through, and is symmetrical with respect to, the associated galaxy1. This structure is sometimes modified to a V or C shape with the galaxy at the apex, as in the wide angle tail sources like 3C465 (ref. 2), and occasionally to the more extreme elongation of the tail sources such as NGC1265 (ref. 3). In a few sources an S-shaped or 180° symmetry is seen. This was first noted in the outer components of Cen A4 and a better example is 3C272.1 (refs 5, 6). Other sources where the S distortion is very clear have been found with higher resolution observations (for example Cyg A7 and 3C478). In these, the structure in question subtends a small angle from the centre and they give a strong impression of a beam type of model in which the beam has wobbled or precessed by a few degrees9. A new example of a radio source showing a structure with a 180° symmetry, but not of the S form, has been found as part of a systematic study of radio galaxies of lower luminosity selected from the B2 catalogue10. The projection of a precessing beam model seems to provide a natural explanation for this strange shape and is described here.

NGC326 - A radio galaxy with a precessing beam

Analysis of new high-resolution radio observations of quasars with redshifts >1.5 shows that these powerful extragalactic radio sources have epoch-dependent physical properties. Distant quasars have a more bent, distorted appearance and are smaller than those nearby. The ambient medium, interacting with the radio jets, is postulated as playing an important role in producing these epoch-dependent effects. Optical absorption line studies are important in this respect. These observations provide an important new probe of young galaxies and their formation.

Evolution of radio structure in quasars: a new probe of protogalaxies?

We have carried out an extensive study of a sample of 13 large, powerful Fanaroff-Riley type II radio galaxies with the Very Large Array in multiple configurations at 330 MHz and 14, 5, and 8 GHz We present the total intensity, polarization, spectral index, and rotation measure maps of the sources On the whole, the 13 FR II sources have symmetric structures with arm-length ratios close to unity, small misalignment angles, and low values of radio core prominence, suggesting that these radio galaxies lie close to the plane of the sky We have revisited some well-known radio galaxy correlations using a large combined data set comprising our radio galaxies and others from the literature We confirm that the hot spot size correlates with the core-hot spot distance The hot spot spectral index is correlated with and flatter than the lobe spectral index, consistent with the assumptions of spectral aging models Both the hot spot and lobe spectral index are correlated with redshift The depolarization asymmetry in the lobes is not correlated with the radio core prominence or misalignment angle, which are statistical indicators of orientation The 'Liu-Pooley' correlation of lobe depolarization with the lobe spectral index is significant in ourmore » radio galaxy sample Furthermore, the lobe with the steeper spectral index and greater depolarization is shorter and fatter The arm-length ratio seems to be correlated with the misalignment angle between the two sides of the radio source and strongly anticorrelated with the axial ratio, consistent with environmental effects and/or a change in the outflow direction In this sample, asymmetries in the local environments and/or motion of the outflow axis are likely to be more important than relativistic beaming effects« less

https://www.cis.rit.edu/~cposps/science/jets/RGs.pdf

A Study of 13 Powerful Classical Double Radio Galaxies

We investigate the relations between the observed emission-line strengths, widths, and continuum properties of a sample of 41 low-redshift (z<1) quasars for which contemporaneous IR/soft X-ray spectral energy distributions are available. This includes investigating correlations between optical and UV lines with both the luminosity and the shape of the quasars' continuum, as well as correlations between the various lines. The sample is heterogeneous, primarily selected on the existence of good-quality Einstein X-ray data, and includes 18 radio-loud and 23 radio-quiet quasars. We find anticorrelations between the equivalent width and various UV luminosities (the Baldwin effect) for the Lyα and Hβ lines and a marginal anticorrelation for C III]. Exclusion of narrow-line, low-luminosity active galactic nuclei reveals a significant Baldwin effect for the C IV and C III] lines. A significant anticorrelation of EW(C IV) with αox is also present. We find no correlations between any lines and the X-ray luminosity or X-ray slope. The Fe II optical multiplet shows no simple relationship with luminosity or continuum slope; however, there is a tendency for objects with flat X-ray spectra and/or strong X-ray luminosities to have weak Fe II. Our data do not favor a model in which changes in continuum shape (due to, e.g., a decreasing ionization parameter) cause the Baldwin effect. The data can instead be explained by an accretion disk (AD) model in which limb darkening and the projected surface area of an optically thick, geometrically thin disk combine to cause a viewing-angle-dependent UV luminosity and a more isotropic X-ray luminosity. The scatter in our correlations is larger than that expected from this AD model, suggesting the presence of dust, which reddens both the continuum and the broad emission lines. The C IV and C III] lines show flatter slopes and larger scatter in the line-continuum relations than predicted by the AD+dusty torus model. This may be due to a significant contribution from collisional excitation that is not directly related to the ionizing continuum.

G. G. Pooley

Papers

Observations of 48 extragalactic radio sources with the Cambridge 5-km telescope at 5 GHz.