scholarly journals Space Densities for Powerful Radio Sources in the Light of Unification

1996 ◽  
Vol 175 ◽  
pp. 553-554
Author(s):  
C.A. Jackson ◽  
J.V. Wall
Keyword(s):  
Line Of Sight ◽  
Radio Sources ◽  
Powerful Radio ◽  
The Core ◽  
Central Maximum ◽  
Spectrum Radio ◽  
Radio Survey

As radio survey frequency is raised the proportion of flat-spectrum sources increases in bright flux-limited samples (eg Wall 1994, Aust J Phys47, 625). Differential source counts show a corresponding broadening of the central maximum due to the increasing proportion of flat-spectrum sources. Orr & Browne (1982, MNRAS200, 1067) modelled this change in shape of the source count by proposing a unifying scheme which states that the core-dominated, flat-spectrum radio sources are the steep-spectrum sources with their cores Doppler-boosted due to the alignment of the jets with the line of sight.

scholarly journals A multiwavelength study of a sample of Texas Radio Survey steep spectrum sources

2006 ◽  
Vol 2 (14) ◽  
pp. 610-610
Author(s):  
Ray A. Lucas ◽  
Neal Miller ◽  
Anton M. Koekemoer ◽  
Jeffrey Van Duyne ◽  
Kenneth C. Chambers
Keyword(s):  
Radio Interferometer ◽  
Radio Sources ◽  
Complete Sample ◽  
Spectrum Radio ◽  
Radio Survey

VLA A-array snapshots were obtained of a complete sample of steep-spectrum radio sources from the Texas Radio Interferometer survey. Though similar in sensitivity to the FIRST Survey, our A-array snapshots have better resolution, and are complementary to FIRST. All initial A-array maps are made, and we are comparing them to FIRST.

Dust Obscuration in the Universe

1995 ◽  
Vol 12 (2) ◽  
pp. 146-152 ◽  
Author(s):  
F. J. Masci ◽  
R. L. Webster
Keyword(s):  
Probability Distribution ◽  
Optical Depth ◽  
Dust Content ◽  
Line Of Sight ◽  
Radio Sources ◽  
Complete Sample ◽  
Spectrum Radio ◽  
The Universe

AbstractA substantial population of red quasars has been discovered in a complete sample of flat-spectrum radio sources. Dust is the most likely cause of the reddening in this sample. The location of the dust is poorly known, but may either be in the line-of-sight to the quasar, or in the immediate quasar environment. In this paper we are interested in models where the dust is located in the line of sight to the quasar. We calculate the probability distribution of the optical depth in galactic dust as a function of source redshift, using a range of parameters which might describe real galaxies. We compare these results with those found for our sample of radio quasars. If the dust content is unevolving, then it is not possible to account for all the observed reddening in the quasar sample using these models. Our minimum dust model predicts that 15% of background quasars to z ~ 5 will have a line of sight within 5 kpc of a galaxy’s centre, and would therefore be reddened out of B-band flux-limited samples.

scholarly journals Morphology of Steep Spectrum Radio Sources Showing Variability at Low Frequency

1988 ◽  
Vol 129 ◽  
pp. 125-126
Author(s):  
Franco Mantovani ◽  
Tom Muxlow ◽  
Lucia Padrielli
Keyword(s):  
Interstellar Medium ◽  
Flux Density ◽  
Large Fraction ◽  
Low Frequency ◽  
Line Of Sight ◽  
Radio Sources ◽  
Relativistic Motion ◽  
High Brightness ◽  
Spectrum Radio ◽  
Low Frequency Variability

The observed variability at low frequency of the radio sources can be explained within the framework of the generally accepted models either extrinsic (refractive scintillation in the interstellar medium) or intrinsic (bulk relativistic motion along direction near the line of sight) for variability. Both explanations require a large fraction of the source flux density to be contained in a small high brightness component, of tens of m.a.s. in size. Radio sources with steep straight spectral index are usually tens of Kpc sized, with weak central components and they do not generally show low frequency variability.

scholarly journals A Radio Survey For Gravitational Lenses In The Southern Hemisphere

1996 ◽  
Vol 173 ◽  
pp. 403-404
Author(s):  
J.E.J. Lovell ◽  
P.M. McCulloch ◽  
D.L. Jauncey
Keyword(s):  
Brightness Temperature ◽  
Southern Hemisphere ◽  
Gravitational Lens ◽  
Radio Sources ◽  
Gravitational Lenses ◽  
High Brightness ◽  
Spectrum Radio ◽  
Compact Array ◽  
Radio Survey

We are undertaking an imaging survey with the Australia Telescope Compact Array (ATCA) to find gravitational lens candidates in flat-spectrum Parkes Catalogue radio sources. Flat-spectrum radio sources typically possess a single high brightness temperature nucleus of milliarcsecond size. Such sources, if lensed, will show multiply imaged nuclei with separations that are large compared to their milliarcsecond sizes. Our flat-spectrum sample was selected using the criteria α2.7/5.0 > −0.5 (S(v) ∝ vα), S2.7 > 0.34Jy and δ ≤ −20°, and comprises a total of 461 sources.

scholarly journals Unveiling the cause of hybrid morphology radio sources (HyMoRS)

2019 ◽  
Vol 491 (1) ◽  
pp. 803-822 ◽  
Author(s):  
Jeremy J Harwood ◽  
Tessa Vernstrom ◽  
Andra Stroe
Keyword(s):  
Radio Galaxies ◽  
Core Region ◽  
Line Of Sight ◽  
Radio Sources ◽  
Large Array ◽  
Very Large Array ◽  
Array Configuration ◽  
The Core ◽  
Vlbi Observations ◽  
Rare Group

ABSTRACT Hybrid morphology radio sources (HyMoRS) are a rare group of radio galaxies in which differing Fanaroff & Riley morphologies (FR I/II) are observed for each of the two lobes. While they potentially provide insights into the formation of lobe structure, particle acceleration, and the FR dichotomy, previous work on HyMoRS has mainly been limited to low-resolution studies, searches for new candidates, and milliarcsecond-scale VLBI observations of the core region. In this paper, we use new multi-array configuration Very Large Array (VLA) observations between 1 and 8 GHz to determine the morphology of HyMoRS on arcsecond scales and perform the first well-resolved spectral study of these unusual sources. We find that while the apparent FR I lobe is centre brightened, this is the result of a compact acceleration region resembling a hotspot with a spectrum more consistent with an FR II (‘strong-flavour’) jet. We find that the spectra of the apparent FR I lobes are not similar to their classical counterparts and are likely the result of line-of-sight mixing of plasma across a range of spectral ages. We consider possible mechanisms that could lead to the formation of HyMoRS under such conditions, including environment asymmetry and restarted sources, concluding through the use of simple modelling that HyMoRS are the result of orientation effects on intrinsically FR II sources with lobes non-parallel to the inner jet.

CTD 93 and the Nature of Gigahertz Peaked Spectrum Radio Sources

1999 ◽  
Vol 515 (2) ◽  
pp. 558-566 ◽  
Author(s):  
David B. Shaffer ◽  
K. I. Kellermann ◽  
T. J. Cornwell
Keyword(s):  
Radio Sources ◽  
Spectrum Radio

scholarly journals Large Bent Jets in the Inner Region of CSS

1996 ◽  
Vol 175 ◽  
pp. 71-72
Author(s):  
F. Mantovani ◽  
W. Junor ◽  
M. Bondi ◽  
L. Padrielli ◽  
W. Cotton ◽  
...  
Keyword(s):  
Velocity Structure ◽  
Radio Sources ◽  
Ambient Media ◽  
The Core ◽  
Gaseous Environment ◽  
Radio Jets ◽  
Large Size ◽  
Superluminal Motion ◽  
Inner Region ◽  
Quasars And Radio Galaxies

Recently we focussed our attention on a sample of Compact Steep-spectrum Sources (CSSs) selected because of the large bent radio jets seen in the inner region of emission. The largest distortions are often seen in sources dominated by jets, and there are suggestions that this might to some extent be due to projection effects. However, superluminal motion is rare in CSSs. The only case we know of so far is 3C147 (Alef at al. 1990) with a mildly superluminal speed of ≃ 1.3v/c. Moreover, the core fractional luminosity in CSSs is ≃ 3% and ≤ 0.4% for quasars and radio galaxies respectively. Similar values are found for large size radio sources i.e. both boosting and orientations in the sky are similar for the two classes of objects. An alternative possibility is that these bent-jet sources might also be brightened by interactions with the ambient media. There are clear indications that intrinsic distortions due to interactions with a dense inhomogeneous gaseous environment play an important role. Observational support comes from the large RMs found in CSSs (Taylor et al. 1992; Mantovani et al. 1994; Junor et al. these proc.) and often associated with strong depolarization (Garrington & Akujor, t.p.). The CSSs also have very luminous Narrow Line Regions emission, with exceptional velocity structure (Gelderman, t.p.).

scholarly journals Active Nuclei and Redshift Problems

1983 ◽  
Vol 6 ◽  
pp. 531-533
Author(s):  
Geoffrey Burbidge
Keyword(s):  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Radio Sources ◽  
Powerful Radio ◽  
Radiation Mechanism ◽  
X Ray ◽  
Major Interest ◽  
Relativistic Particles

More than 20 years ago V. A. Ambartsumian proposed that much of the activity in galaxies was dominated and even generated by their nuclei. Subsequent observational work in radio, optical and x-ray frequencies has borne out his prophecy, and major interest has centered about the nature of the machine in the galactic nucleus. The major characteristic of this machine is that it releases energy rapidly and often spasmodically by processes which are not thermonuclear in origin.The original studies which led to the conclusion that nuclei were all important were observations of the powerful radio sources and Seyfert galaxies, and evidence for the ejection of gas from galaxies of many types. The realization that the synchrotron mechanism was the dominant radiation mechanism and the later studies of Compton radiation were fundamental in leading to the conclusion that large fluxes of relativistic particles must be generated in galactic nuclei.

scholarly journals Bulk Relativistic Motion in a Complete Sample of Radio Selected AGN

1987 ◽  
Vol 121 ◽  
pp. 287-293
Author(s):  
C.J. Schalinski ◽  
P. Biermann ◽  
A. Eckart ◽  
K.J. Johnston ◽  
T.Ph. Krichbaum ◽  
...  
Keyword(s):  
Dynamic Range ◽  
Radio Sources ◽  
Relativistic Motion ◽  
Complete Sample ◽  
Superluminal Motion ◽  
Spectrum Radio ◽  
Wide Range ◽  
Show Evidence

A complete sample of 13 flat spectrum radio sources is investigated over a wide range of frequencies and spatial resolutions. SSC-calculations lead to the prediction of bulk relativistic motion in all sources. So far 6 out of 7 sources observed with sufficient dynamic range by means of VLBI show evidence for apparent superluminal motion.

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