scholarly journals Spectral Index Studies of Extragalactic Radio Sources

1977 ◽  
Vol 74 ◽  
pp. 99-106
Author(s):  
P. Katgert ◽  
L. Padrielli ◽  
J. K. Katgert ◽  
A. G. Willis
Keyword(s):  
Flux Density ◽  
Spectral Index ◽  
Radio Sources ◽  
Complex Behaviour ◽  
High Frequencies ◽  
Detailed Specification ◽  
Source Sample ◽  
The Mean ◽  
5 Ghz ◽  
Frequency Variations

Spectral index distributions can be indicated conveniently by gSv1(αv1,v2), i.e. the distribution of the two-point spectral index between frequencies v1 and v2 for a sample of radio sources complete to flux density S at the selection frequency v1 (flux densities will be expressed in Jy and frequencies in GHz). Such a detailed specification is necessary because g(α) has been found to depend on all three parameters. The effect of varying v1 is well-known: the fraction of flat-spectrum sources increases with selection frequency. Variations of g(α) with S have also been found: both the fraction of flat-spectrum sources and the mean spectral index of the steep-spectrum sources depend on S, at least at high frequencies. The magnitude of this dependence on S as well as g(α) itself appear to depend on the choice of v2, or rather on the relation between v2 and v1. This complex behaviour of g(α) is not unexpected if one considers that the redshift and luminosity distributions of a source sample vary with selection frequency and flux density limit. Intrinsic or induced correlations between spectral index and redshift or luminosity, or different redshift distributions of flat-and steep-spectrum sources may cause variations of g(α) with v and S. An understanding of the behaviour of g(α) requires observations over large ranges of frequency and flux density. Even then, it will be difficult to interpret these data without information about the composition of the various samples, which can be obtained only through optical work. Here we describe recent spectral index information for weak sources selected at 1.4 GHz, as well as work on spectral index/optical identification correlations in 5 GHz samples.

scholarly journals Number Counts and Spectral Distribution of Radio Sources at Centimeter Wavelengths

1972 ◽  
Vol 44 ◽  
pp. 444-452 ◽  
Author(s):  
I. I. K. Pauliny-Toth ◽  
K. I. Kellermann ◽  
M. M. Davis
Keyword(s):  
Flux Density ◽  
Spectral Index ◽  
Excellent Agreement ◽  
Spectral Distribution ◽  
Low Frequency ◽  
Systematic Change ◽  
Radio Sources ◽  
Significant Dependence ◽  
5 Ghz ◽  
Number Counts

The results of a survey of selected regions of sky made at a frequency of 5 GHz, and of measurements of the spectral index distributions for sources selected from low frequency surveys are presented. The source counts and spectral distribution at 5 GHz are in excellent agreement with those expected from surveys made at lower frequencies. There is no significant dependence of the spectral distribution on flux density in any of the surveys we have investigated, implying either a low redshift for the sources, or a systematic change in their properties with redshift.

scholarly journals A Catalogue of Galactic Radio Sources

1968 ◽  
Vol 21 (3) ◽  
pp. 369 ◽  
Author(s):  
MJL Kesteven
Keyword(s):  
Flux Density ◽  
Spectral Index ◽  
Galactic Plane ◽  
Radio Sources ◽  
Galactic Radio

The results of a survey of radio sources in the galactic plane in the longitude range 1800 to 400 with the 1 mile Molonglo Cross telescope at 408 MHz are presented. The methods of observation and reduction are described briefly. The catalogue lists the position, flux density, size, and spectral index for 80 sources

scholarly journals VLBI Survey of a Complete Sample of Active Nuclei and Quasars

1984 ◽  
Vol 110 ◽  
pp. 15-24 ◽  
Author(s):  
T. J. Pearson ◽  
A.C.S. Readhead
Keyword(s):  
Flux Density ◽  
Radio Sources ◽  
Complete Sample ◽  
Limited Sample ◽  
Extragalactic Radio Sources ◽  
5 Ghz ◽  
Number Of Classes ◽  
Compact Sources ◽  
Continuous Range

We have conducted a VLBI survey of a complete, flux-density limited sample of 65 extragalactic radio sources, selected at 5 GHz. We have made hybrid maps at 5 GHz of all of the sources accessible to the Mark-II system. The sources can be divided provisionally into a number of classes with different properties: central components of extended double sources, steep-spectrum compact sources, very compact (almost unresolved) sources, asymmetric sources (sometimes called “core-jet” sources), and “compact double” sources. It is not yet clear whether any of these classes is physically distinct from the others, or whether there is a continuous range of properties.

On the Spectral Index-Flux Density Relation for Large Samples of Radio Sources

2003 ◽  
Vol 3 (4) ◽  
pp. 347-358 ◽  
Author(s):  
Xi-Zhen Zhang ◽  
W. Reich ◽  
P. Reich ◽  
R. Wielebinski
Keyword(s):  
Flux Density ◽  
Spectral Index ◽  
Radio Sources ◽  
Large Samples ◽  
Density Relation

scholarly journals Bulk Relativistic Motion in a Complete Sample of Flat Spectrum Radio Sources

1988 ◽  
Vol 129 ◽  
pp. 71-72
Author(s):  
C. J. Schalinski ◽  
A. Witzel ◽  
Th.P. Krichbaum ◽  
C. A. Hummel ◽  
P. L. Biermann ◽  
...  
Keyword(s):  
Flux Density ◽  
Status Report ◽  
Radio Sources ◽  
Supporting Evidence ◽  
X Rays ◽  
Relativistic Motion ◽  
Bl Lac Objects ◽  
Vlbi Observations ◽  
Wide Range ◽  
5 Ghz

As part of a multi-epoch and multi-wavelength study of the physics of core dominated radio sources we have investigated the occurrence of apparent superluminal motion and other indications for bulk relativistic motion (b.r.m) in a statistically complete, flux density limited (S5GHz ≥ 1Jy) sample of 13 objects with flat radio spectra These sources come from the S5-survey (Kühr et al., 1981) and are optically identified as 7 quasars and 6 BL-Lac objects. They have been observed over a wide range of frequencies, from radio through X-rays (s. Eckart et al., 1986 and references therein). Radiomaps have been obtained at frequencies from 327 MHz to 22.2 GHz with resolutions from arcseconds to 0.2 mas, using the VLA, MERLIN and telescopes of the US- and European-VLBI networks. A recent status report on the VLBI-observations is given by Witzel (1987). In this paper we summarize the results on the direct evidence for b.r.m. in this sample as derived from repeated VLBI-observations at 5 GHz, as well as supporting evidence from SSC-calculations and flux density variability of the 5GHz VLBI core components (Table 1).

scholarly journals Spectral Index - Redshift Relation for Radio Galaxies and Quasars

1996 ◽  
Vol 175 ◽  
pp. 569-570
Author(s):  
R.D. Dagkesamanskii
Keyword(s):  
Flux Density ◽  
Spectral Index ◽  
Low Frequency ◽  
Radio Galaxies ◽  
Cosmological Evolution ◽  
Radio Sources ◽  
Spectral Indices ◽  
Extragalactic Radio Sources

Cosmological evolution of synchrotron spectra of the powerful extragalactic radio sources was studied by many authors. Some indications of such an evolution had been found firstly by analysis of ‘spectral index - flux density’ (α – S) relation for the sample of relatively strong radio sources. Later Gopal-Krishna and Steppe extended the analysis to weaker sources and found that the slope of αmed(S) curve changes dramatically at intermediate flux densities. Gopal-Krishna and Steppe pointed out that the maxima of the αmed(S) curve and of differential source counts are at almost the same flux density ranges (see, Fig. 2). It has to be noticed that the all mentioned results were obtained using the low-frequency spectral indices and on the basis of low frequency samples.

scholarly journals Unveiling the high-frequency radio source population with the AT20G survey

2013 ◽  
Vol 9 (S304) ◽  
pp. 205-208
Author(s):  
Elizabeth K. Mahony
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
High Frequency ◽  
Gamma Ray ◽  
Low Frequency ◽  
Radio Sources ◽  
Source Population ◽  
Frequency Source ◽  
Galaxy Population ◽  
5 Ghz

AbstractUntil recently, the radio sky above 5 GHz was relatively unexplored. This has changed with the completion of the Australia Telescope 20 GHz survey (AT20G; Murphy et al., 2010); a blind survey of the southern sky down to a limiting flux density of 40 mJy. The AT20G survey provides by far the largest and most complete sample of high-frequency radio sources yet obtained, offering new insights into the nature of the high-frequency active galaxy population. Whilst the radio data provides a unique sample of objects, these data alone are insufficient to completely constrain models of radio source properties and the evolution of radio galaxies. Complementary multiwavelength data is vital in understanding the physical properties of the central black hole.In this talk I will provide a brief overview of the AT20G survey, followed by a discussion of the multiwavelength properties of the high-frequency source population. In particular, I will focus on the optical properties of AT20G sources, which are very different to those of a low-frequency selected sample, along with the gamma-ray properties where we find a correlation between high-frequency radio flux density and gamma-ray flux density. By studying the multiwavelength properties of a large sample of high-frequency radio sources we gain a unique perspective on the inner dynamics of some of the most active AGN.

scholarly journals Evolution of the Radio Emission from Young SNRs according to Observational Data

1979 ◽  
Vol 32 (2) ◽  
pp. 95 ◽  
Author(s):  
KS Stankevich
Keyword(s):  
Experimental Data ◽  
Radio Emission ◽  
Flux Density ◽  
Observational Data ◽  
Spectral Index ◽  
Density Measurements ◽  
The Past ◽  
Absolute Flux ◽  
Density Decrease ◽  
Frequency Variations

Results are given from a still-continuing series of absolute flux density measurements for the SNR CasA. The measurements have been taken regularly over the past 16 years at 24 wavelengths in the range 3-60 cm. New data are presented for the rate of flux density decrease, and for time and frequency variations in the spectral index. Intensity increases that are localized in frequency are described. The results are generalized in a model for the radio emission from a young SNR, and this is used to analyse experimental data for flux density decreases in the emission from 3C 10 and 58.

scholarly journals Surveys of Radio Sources at 5 GHz

1977 ◽  
Vol 74 ◽  
pp. 63-74
Author(s):  
I. I. K. Pauliny-Toth
Keyword(s):  
Flux Density ◽  
Radio Astronomy ◽  
Radio Sources ◽  
Astronomy Observatory ◽  
Max Planck ◽  
Radio Astronomy Observatory ◽  
Density Relation ◽  
Strong Source ◽  
Optical Identifications ◽  
5 Ghz

A number of surveys have been carried out at a frequency of 5 GHz at the National Radio Astronomy Observatory (NRAO) and at the Max-Planck-Institut für Radioastronomie (MPIfR), with the aim of determining the number-flux density relation for the sources detected and also of obtaining their radio spectra and optical identifications. The surveys fall into two categories: first, the strong source (S) surveys, which are intended in due course to cover the whole northern sky and to be complete above a flux density of about 0.6 Jy; second, surveys of limited areas of sky down to lower levels of the flux density.

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