scholarly journals Australian Journal of Physics Astrophysical Supplement

1973 ◽  
Vol 26 (1) ◽  
pp. 115
Author(s):  
OB Slee ◽  
CS Higgins
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
Australian Journal ◽  
Radio Sources ◽  
Success Rates ◽  
Low Resolution ◽  
Upper Limits

The Culgoora radioheliograph operating at 80 MHz has been used to observe 999 radio sources selected from published catalogues and distributed over the declination range -48� to +35�. The Culgoora-l list contains measurements with 3' . 7 arc resolution of positions, flux densities, and angular sizes of 777 sources, while upper limits to the flux densities of 222 undetected sources are given in a separate list. Success rates for the detection of various classes of radio source at 80 MHz are listed and discussed. Comparisons are made between the Culgoora flux densities and those given in other catalogues, and it is shown that unresolved sources in the earlier low-resolution measurements near 80 MHz cause the flux density to be systematically overestimated.

scholarly journals VLBA+GBT observations of the COSMOS field and radio source counts at 1.4 GHz

2018 ◽  
Vol 616 ◽  
pp. A128 ◽  
Author(s):  
N. Herrera Ruiz ◽  
E. Middelberg ◽  
A. Deller ◽  
V. Smolčić ◽  
R. P. Norris ◽  
...  
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
Lower Limit ◽  
High Sensitivity ◽  
Host Galaxy ◽  
Radio Sources ◽  
Source Population ◽  
Star Forming ◽  
Brightness Temperatures ◽  
Long Baseline

We present very long baseline interferometry (VLBI) observations of 179 radio sources in the COSMOS field with extremely high sensitivity using the Green Bank Telescope (GBT) together with the Very Long Baseline Array (VLBA) (VLBA+GBT) at 1.4 GHz, to explore the faint radio population in the flux density regime of tens of μJy. Here, the identification of active galactic nuclei (AGN) is based on the VLBI detection of the source, meaning that it is independent of X-ray or infrared properties. The milli-arcsecond resolution provided by the VLBI technique implies that the detected sources must be compact and have large brightness temperatures, and therefore they are most likely AGN (when the host galaxy is located at z ≥ 0.1). On the other hand, this technique only allows us to positively identify when a radio-active AGN is present, in other words, we cannot affirm that there is no AGN when the source is not detected. For this reason, the number of identified AGN using VLBI should be always treated as a lower limit. We present a catalogue containing the 35 radio sources detected with the VLBA+GBT, ten of which were not previously detected using only the VLBA. We have constructed the radio source counts at 1.4 GHz using the samples of the VLBA and VLBA+GBT detected sources of the COSMOS field to determine a lower limit for the AGN contribution to the faint radio source population. We found an AGN contribution of >40−75% at flux density levels between 150 μJy and 1 mJy. This flux density range is characterised by the upturn of the Euclidean-normalised radio source counts, which implies a contribution of a new population. This result supports the idea that the sub-mJy radio population is composed of a significant fraction of radio-emitting AGN, rather than solely by star-forming galaxies, in agreement with previous studies.

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 Australian Journal of Physics Astrophysical Supplement

1976 ◽  
Vol 29 (5) ◽  
pp. 471
Author(s):  
JN Clarke ◽  
AG Little ◽  
BY Mills
Keyword(s):  
Flux Density ◽  
High Frequency ◽  
Magellanic Clouds ◽  
Australian Journal ◽  
The Other ◽  
Optical Data ◽  
Radio Sources ◽  
Angular Extent

The fourth catalogue of radio sources observed at 408 MHz with the Molonglo radiotelescope is presented. A total of 1349 sources is listed to a limiting flux density of 0�2 Jy, the catalogue being largely complete above 0� 25 Jy. The area of sky surveyed includes the Magellanic Clouds as well as a comparison region of similar angular extent. Detailed notes are provided on some of the Cloud sources, and maps are given for complex sources in the region of the Clouds. Those sources for which high-frequency or optical data are available are classified into two lists, one of Cloud members and the other of 'unidentified nonthermal sources', presumably not Cloud members.

scholarly journals The Radio Spectrum of SGR A∗

1996 ◽  
Vol 171 ◽  
pp. 342-342 ◽  
Author(s):  
T. Beckert ◽  
W.J. Duschl ◽  
P.G. Mezger ◽  
R. Zylka
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
Radio Spectrum ◽  
Frequency Range ◽  
Upper Limits ◽  
The Galaxy ◽  
Sgr A

Sgr A∗, the enigmatic radio source located at the dynamical center of the Galaxy, is firmly detected in the frequency range of ∼ 1 – few 102 GHz. For ∼ 0.5 – 1 GHz and in the MIR range only significant upper limits of the flux density are known. Between ∼ 1.5 and 600 GHz the time averaged flux density Sv is proportional to v1/3 (v: frequency). For frequencies higher than ∼ 600 GHz as well as for those lower than ∼ 1.5 GHz, Sv drops sharply.

A Confusion Limited Radio Survey from the Molonglo Cross

1984 ◽  
Vol 5 (3) ◽  
pp. 290-340 ◽  
Author(s):  
Graeme L. White
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
Radio Sources ◽  
Chronological Order ◽  
Extragalactic Radio Sources ◽  
Density Limit ◽  
Sky Survey ◽  
Radio Survey

Several catalogues of radio sources at 408 MHz have been prepared from observations made with the Molonglo cross telescope. These include (in chronological order) ‘The Molonglo Radio Source Catalogue 1’, the MC1, by Davies et al. (1973), the MC2 and MC3 by Sutton et al. (1974), MC4 by Clarke et al. (1976), ‘The Molonglo Deep Sky Survey of Radio Sources’ by Robertson (1977a,b,d) and ‘The Molonglo Reference Catalogue of Radio Sources’ (MRC) by Large et al. (1981). The catalogues MC1-4 cover selected areas of sky to a flux density limit of ~0.2 Jy to 0.3 Jy. The MRC includes extragalactic radio sources between δ = +18° and δ = −85° and is essentially complete at S408 = 1.00 Jy with raany sources to ˜0.7 Jy. The Wyllie (1969a,b) scale of flux density is used throughout.

scholarly journals Australian Journal of Physics Astrophysical Supplements

1973 ◽  
Vol 26 (5) ◽  
pp. 689
Author(s):  
M Davies ◽  
AG Little ◽  
BY Mills
Keyword(s):  
Flux Density ◽  
Australian Journal ◽  
Radio Sources

A catalogue of radio sources observed at a frequency of 408 MHz with the Molonglo radiotelescope is presented. The catalogue includes an area of 0�21 sr between declinations -19�.3 and - 22� �4. A total of 1545 sources is listed down to a limiting flux density of O� 1 f.u., the catalogue being largely complete above 0�25 f.u. Errors in position vary from ~ 5N arc for sources stronger than 1 f.u. to ~ 30N arc for the weakest sources.

scholarly journals Cosmological Size Evolution of Extragalactic Radio Sources

1996 ◽  
Vol 175 ◽  
pp. 563-566
Author(s):  
Ashok K. Singal
Keyword(s):  
Radio Source ◽  
Size Distribution ◽  
Flux Density ◽  
Angular Size ◽  
Radio Sources ◽  
Source Population ◽  
Extragalactic Radio Source ◽  
Quarter Century ◽  
Extragalactic Radio Sources ◽  
Size Evolution

The study of cosmological evolution of the sizes of extragalactic radio sources started about a quarter century back. From the very first angular size-redshift (θ-z) plots (Miley 1968, 1971; Legg 1970) and angular size-flux density (θ-S) plots (Swarup 1975; Kapahi 1975) it became evident that some sort of cosmic epoch-dependent evolution in the size distribution for the population of extragalactic radio source needs to be proposed; the sources at earlier epochs appeared on the average to have smaller physical sizes. However, a suitable luminosity-linear size (P-l) correlation among the radio source population could also explain the observations, without invoking a size evolution with redshift. The only reliable way to disentangle these two separate effects is to investigate the size distribution in the luminosity-redshift plane, where one could examine not only the l-z relation for a given luminosity class, but could also check for a P-l correlation in a given redshift bin.

scholarly journals Radio Source Counts at Centimetre Wavelengths

1974 ◽  
Vol 63 ◽  
pp. 111-119 ◽  
Author(s):  
I. I. K. Pauliny-Toth ◽  
K. I. Kellermann
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
Radio Sources ◽  
Sharp Drop ◽  
Integral Number ◽  
Cosmic Evolution ◽  
Strong Source ◽  
5 Ghz ◽  
Number Counts

Counts of radio sources at 5 GHz (6 cm wavelength) have been derived from a number of surveys including a new strong source survey. The source counts do not appear to differ markedly from an integral number-flux relation having a slope of − 1.5 between 5 and 5 × 103 sources per steradian, and show a sharp drop at source densities smaller than 5 sr-1. On the basis of the form of the number counts and the observed anisotropies in the distribution of sources and of their spectra, the cosmological significance of the source counts is questioned. In particular, the evidence for strong cosmic evolution appears weaker than is generally thought unless the cosmological origin of the quasar redshifts is assumed. Measurements of the radio spectra of the sources suggest a dependence of the spectral curvature on flux density.

scholarly journals Australian Journal of Physics Astrophysical Supplements

1977 ◽  
Vol 30 (6) ◽  
pp. 681
Author(s):  
C Hazard ◽  
HS Murdoch
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
Spectral Sensitivity ◽  
Australian Journal ◽  
Magnitude Distribution ◽  
Sky Survey ◽  
Magnitude Scales

This paper presents the results of an examination of the fields around 350 sources in the Molonglo radio source catalogues MC2 and MC3 for the R.A. interval 11 h 28m to 17h oom. The 300 sources with a flux density ;;. 0�45 Jy form an essentially complete radio sample and of these 21 % are identified with BSOs (most of which have now been spectroscopically confirmed as QSOs) and 22 % with galaxies of Ism or brighter. The magnitude scales adopted are carefully defined and based on the spectral sensitivity of the Palomar Sky Survey plates. A brief discussion is given of the magnitude distribution of the BSO identifications and possible evidence for anisotropy in the QSO distribution is noted.

scholarly journals Australian Journal of Physics Astrophysical Supplement

1975 ◽  
Vol 28 (6) ◽  
pp. 755
Author(s):  
Beverley J Wills
Keyword(s):  
Flux Density ◽  
Australian Journal ◽  
Radio Sources

Accurate measurements of relative flux density have been made between frequencies of 468 and 5009 MHz for 300 radio sources selected from the Parkes catalogue. The observations, their analysis and accuracy are described, and the flux densities presented together with their errors. Excluding the uncertainties in scaling these flux densities to an absolute system, r.m.s. errors vary from 0�24 Jy and 2�4 % at 635 MHz to 1�8 % at 2700 MHz; uncertainties in 'absolute' scaling are thought to be about 5 %. The present flux densities are compared with accurate values published elsewhere. The data have been combined with other published flux densities between 10 and 10000 MHz to derive spectra, which are presented graphically. Some sources whose spectra may be useful for flux density calibration are noted.

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