Cosmology: discrete radio sources and gravitational lensing

Since nearly all discrete radio sources of astronomical interest are of insufficient angular extent for their detailed structural properties to be accessible to single-dish radio telescopes, radio interferometry must be employed to gain information on the morphologies of these objects. Recently constructed imaging interferometer arrays which employ the technique of Fourier synthesis, particularly MERLIN and the VLA (Very Large Array), and the more recent VLBI arrays, have given unprecedented imaging capabilities, with the result that our knowledge, and hence perceptions, of discrete radio sources have vastly changed over the last few years. An equally important parallel development has been image processing algorithms. These have vastly improved the quality of information produced by these arrays, so that an instrument such as the VLA can now produce images with speed and quality exceeding original design specifications by factors of 100 to 1000.

Discrete Radio Sources in the Spiral Galaxy NGC 6946

The Astronomical Journal ◽

10.1086/301306 ◽

2000 ◽

Vol 119 (4) ◽

pp. 1711-1719 ◽

Cited By ~ 12

Author(s):

Scott D. Hyman ◽

Christina K. Lacey ◽

Kurt W. Weiler ◽

Schuyler D. Van Dyk

Keyword(s):

Spiral Galaxy ◽

Radio Sources ◽

Ngc 6946 ◽

Discrete Radio Sources

Observations of Linear Polarization of Fifty-Four Discrete Radio Sources at 10.6 CM

The Astrophysical Journal ◽

10.1086/148597 ◽

1966 ◽

Vol 144 ◽

pp. 216 ◽

Cited By ~ 2

Author(s):

P. Maltby ◽

G. A. Seielstad

Keyword(s):

Linear Polarization ◽

Radio Sources ◽

Discrete Radio Sources

PKS 1117+146: Gravitational Lens or Micro lobes

Symposium - International Astronomical Union ◽

10.1017/s0074180900080256 ◽

1996 ◽

Vol 175 ◽

pp. 118-119

Author(s):

M. Bondi ◽

M. Garrett ◽

L. Gurvits

Keyword(s):

Gravitational Lensing ◽

Hot Spot ◽

Low Frequency ◽

Gravitational Lens ◽

Central Component ◽

Radio Sources ◽

Double Structure ◽

Global Arrays ◽

Low Frequency Variability ◽

First Time

PKS 1117+146 is a high power radio source (L327MHz=5.4 × 1026 W/Hz) identified with a galaxy of 20.1 red magnitude at z=0.362 (de Vries et al. 1995). At this redshift 1 mas ≃ 2.9 pc (H0 = 100 km/s–1Mpc–1). Based on the properties of the radio spectra, PKS 1117+146 is classified as a GigaHertz Peaked Spectrum source (GPS) (Stanghellini et al. 1990). The GPS are powerful but physically small (sub-galactic sizes) radio sources with turnovers in their radio spectra at v ≃ 1 GHz. They are supposed to be isotropically emitting radio sources confined by exceptional dense circumnuclear gas (O'Dea et al. 1991) or still relatively young (Fanti et al. 1990). PKS 1117+146 is also a low frequency variable (LFV) with no sign of variability at v > 1 GHz (Padrielli et al. 1987, Mitchell et al. 1994). The low frequency variability is caused by propagation effects in the interstellar medium of our Galaxy (Mantovani et al. 1990, Spangler et al. 1993). PKS 1117+146 was observed with VLBI global arrays at 608 MHz (Padrielli et al. 1991), at 327 MHz (Altschuler et al. 1995), and at 1667 MHz (Bondi et al. 1996). All the maps are in agreement showing a compact double structure with components separated by about 70 mas. Flux densities and separation of the two components derived from VLBI and MERLIN (see below) maps are listed in Table 1. The flux ratios of the two components from the VLBI observations are very similar, and the spectral index is relatively flat (α ≃ 0.3–0.4), even if the strong low frequency variability can introduce uncertainties. The similarity of the VLBI morphology and spectral properties of the two components suggested that 1117+146 could be a possible gravitational lens candidate prompting for higher frequency observations. We observed PKS 1117+146 with MERLIN at 22 GHz in March 1993. MERLIN observations reveal for the first time a weak central component with a total flux density of about 20 mJy (Fig.1). From Table 1 we can note that the P.A. between the components is constant at all the frequencies while the separation between the peak flux densities significantly increases at higher frequencies. This is the expected behaviour if the 2 components are 2 lobes with hot-spot at the outer edges. The MERLIN map at 22 GHz seems to rule out the possibility that the morphology of PKS 1117+146 is caused by gravitational lensing.

Association Of Distant Radio Sources And Foreground Galaxies

Symposium - International Astronomical Union ◽

10.1017/s0074180900230970 ◽

1996 ◽

Vol 173 ◽

pp. 83-88

Author(s):

E. Martínez-González ◽

N. Benítez

Keyword(s):

Gravitational Lensing ◽

Large Scale ◽

Radio Sources ◽

Weak Gravitational Lensing ◽

Large Scale Structures ◽

Scale Structures ◽

Red Galaxies ◽

Intermediate Redshifts

A statistically significant (99.1%) excess of red galaxies from the APM Sky Catalogue is found around a sample of z ∼ 1 1Jy radio sources. The most plausible explanation for this result seems to be the magnification bias caused by the weak gravitational lensing of large scale structures at intermediate redshifts.

Apparent Angular Sizes of Discrete Radio Sources: Observations at Sydney

Nature ◽

10.1038/1701063a0 ◽

1952 ◽

Vol 170 (4338) ◽

pp. 1063-1064 ◽

Cited By ~ 35

Author(s):

B. Y. MILLS

Keyword(s):

Radio Sources ◽

Discrete Radio Sources

The spectra of some discrete radio sources in 10?5000 MHz frequency range

Astrophysics and Space Science ◽

10.1007/bf00650891 ◽

1970 ◽

Vol 8 (2) ◽

pp. 275-322 ◽

Cited By ~ 10

Author(s):

S. Ya. Braude ◽

A. V. Megn ◽

B. P. Ryabov ◽

I. N. Zhouck

Keyword(s):

Radio Sources ◽

Frequency Range ◽

Discrete Radio Sources

Measurements Of The Flux Density Of Discrete Radio Sources At 6 Cm Wavelength

Australian Journal of Physics ◽

10.1071/ph660577 ◽

1966 ◽

Vol 19 (4) ◽

pp. 577 ◽

Cited By ~ 3

Keyword(s):

Flux Density ◽

Radio Telescope ◽

Power Law ◽

Radio Sources ◽

Frequency Range ◽

Thermal Radio ◽

Discrete Radio Sources ◽

Selection Of ◽

Lower Frequencies

The flux densities of 67 non-thermal radio sources have been measured at a frequency of 5000 Mc/s with the CSIRO 210 ft radio telescope at Parkes. The sources were chosen from the stronger objects in the 3C catalogue (Edge et al. 1959), the CTA and CTD catalogues (Harris and Roberts 1960; Kellermann and Read 1965), and the Parkes catalogue (Bolton, Gardner, and Mackey 1964; Price and Milne 1965; Day et al. 1966). In the selection of sources observed in this program, special emphasis was placed on objects whose spectra at lower frequencies showed significant departures from the usual power law with an index near -0�8. Most of the sources reported here have not been previously measured at wavelengths shorter than 10 cm and thus the present observations extend the frequency range of their spectra by nearly a factor of two.

Novel Interferometer for Studies of Discrete Radio Sources.

The Astronomical Journal ◽

10.1086/108838 ◽

1962 ◽

Vol 67 ◽

pp. 575

Author(s):

James N. Douglas ◽

Clinton C. Brooks

Keyword(s):

Radio Sources ◽

Discrete Radio Sources

28. The angular diameter of discrete radio sources

Symposium - International Astronomical Union ◽

10.1017/s0074180900049032 ◽

1957 ◽

Vol 4 ◽

pp. 162-165

Author(s):

H. P. Palmer

Keyword(s):

Resolving Power ◽

Angular Diameter ◽

Radio Sources ◽

Discrete Radio Sources ◽

Angular Diameters

An interferometer of readily varied resolving power has been constructed at Jodrell Bank, and since 1953 it has been used to measure the angular diameters of all but the faintest of the discrete sources reported in the survey of Brown and Hazard [1].