Powerful Radio Sources in Clusters of Galaxies

1991 ◽  
Vol 9 (1) ◽  
pp. 100-102
Author(s):  
A. M. Unewisse ◽  
R. W. Hunstead
Keyword(s):  
Radio Emission ◽  
Radio Source ◽  
Flux Density ◽  
Radio Sources ◽  
High Flux ◽  
Clusters Of Galaxies ◽  
Powerful Radio ◽  
Complete Sample ◽  
Cluster Galaxies ◽  
Cluster Centre

AbstractUsing a complete sample, we have looked for correlations in position between radio sources with S408 ≥ 1 Jy in the Molonglo Reference Catalogue (MRC) and rich clusters of galaxies in the Abell, Corwin and Olowin catalogue (ACO). Within a projected radius of 100 kpc of the cluster centre, we find an overdensity of radio sources similar to that seen by Robertson and Roach (1990). They attributed this feature to centrally located dominant cluster galaxies. We confirm this hypothesis by looking at the morphology of the clusters within this peak and by optically identifying galaxies associated with the radio emission. Due to the relatively high flux density limit imposed, the cluster radio sources in this sample are among the most powerful in the southern sky. The probability of a cluster containing a radio source of this power is found not to depend on cluster richness.

scholarly journals Radio Sources in Clusters of Galaxies

1968 ◽  
Vol 21 (4) ◽  
pp. 511 ◽  
Author(s):  
BY Mills ◽  
RR Shobbrook ◽  
D Stewart-Richardson
Keyword(s):  
Radio Emission ◽  
Radio Source ◽  
Radio Sources ◽  
Clusters Of Galaxies ◽  
Cluster Galaxy ◽  
Stellar Objects ◽  
Cluster Emission ◽  
Cluster Galaxies ◽  
Individual Cluster

Fifty-eight clusters from Abell's catalogue have been examined for radio emission using the Arecibo l000 ft reflector and the Molonglo 1 mile Cross. The positions, sizes, and flux densities at 408 MHz of 30 radio sources close to these clusters have been measured. Nineteen of these offer reasonable identifications with galaxies or blue stellar objects. Thirteen appear to be identifiable with individual cluster galaxies. No evidence for integrated cluster emission has been obtained. It has been concluded that either the centroid of radio sources may sometimes be well displaced from the parent galaxies or, in a significant number of cases, the only detectable radio source in a cluster is associated with a faint cluster galaxy, not a giant.

A Radio Continuum Survey of Southern E and SO Galaxies at 2.7 GHz and 5.0 GHz

1982 ◽  
Vol 4 (4) ◽  
pp. 454-456
Author(s):  
E. M. Sadler
Keyword(s):  
Radio Emission ◽  
Radio Source ◽  
External Factor ◽  
Elliptical Galaxies ◽  
Radio Continuum ◽  
Radio Sources ◽  
Gravitational Perturbation ◽  
Early Type ◽  
Powerful Radio ◽  
Central Source

The reason why some early-type galaxies contain powerful radio sources is not yet well understood, but it is often suggested that an external factor such as interaction with a neighbouring galaxy may be involved in triggering a radio source (Gisler 1976, Dressel 1981, Hummel 1981b). Radio emission may be enhanced in galaxies which have a close companion for several reasons, such as a gravitational perturbation or the possibility of gas accreted from the companion fuelling a central source. The latter effect might be expected to be more pronounced in elliptical galaxies, which are generally gas-poor (Faber and Gallagher 1976).

scholarly journals Variability Observations of a Complete Sample of Flat-Spectrum Radio Sources: Preliminary Results

2001 ◽  
Vol 182 ◽  
pp. 93-96
Author(s):  
A.G. Gorshkov ◽  
V.K. Konnikova ◽  
M.G. Mingaliev
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
Time Scale ◽  
Radio Sources ◽  
Complete Sample ◽  
Limited Sample ◽  
Preliminary Results ◽  
Spectrum Radio ◽  
Intrinsic Mechanism ◽  
Short Time

AbstractThis report presents preliminary results of daily observations, over 60 and 100 days, of a complete, flux-limited sample of radio sources with flat spectra. The existence of flicker up to 21.7 GHz was confirmed, for sources with flat spectra, on a time-scale of 4 days. A model explaining the flux density variations of the unique radio source 0524+034, on long and short time-scales, by an intrinsic mechanism is proposed.

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.

Four Southern Intraday Variable Radio Sources

1998 ◽  
Vol 164 ◽  
pp. 271-272 ◽  
Author(s):  
L. L. Kedziora-Chudczer ◽  
D. L. Jauncey ◽  
M. H. Wieringa ◽  
J. E. Reynolds ◽  
A. K. Tzioumis
Keyword(s):  
Flux Density ◽  
Progress Report ◽  
Radio Sources ◽  
High Flux ◽  
Inverted Spectrum ◽  
Spectrum Radio ◽  
Variable Radio

AbstractThis is a progress report on the ATCA IDV survey of compact, flat or inverted spectrum radio sources. We found that four sources: PKS 0405–385, PKS 1034–293, PKS 1144–397, and PKS 1519–273 out of the sample of 125 show high flux density variability on the daily timescale. The characteristics of observed IDV are discussed and we reflect on its possible origin.

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.

scholarly journals Clusters with extended radio emission at high frequencies

1978 ◽  
Vol 79 ◽  
pp. 157-159
Author(s):  
R. Wielebinski
Keyword(s):  
Radio Emission ◽  
Direct Measurement ◽  
Radio Sources ◽  
Clusters Of Galaxies ◽  
Coma Cluster ◽  
Extended Source ◽  
High Frequencies ◽  
Extended Radio ◽  
Extended Component ◽  
Perseus Cluster

The existence of ‘haloes’ in clusters of galaxies was deduced by Ryle and Windram (1968) for the Perseus cluster and by Willson (1970) for the Coma cluster at 408 MHz by comparing total flux measured by a single dish with the sum of fluxes of radio sources found in the field. A direct measurement of the extended source Coma C was made by Jaffe et al. (1976) at 610 MHz. the failure to detect the halo of Coma at higher frequencies is attributed by all authors to a steep spectrum of this extended component.

scholarly journals Radio properties of a ‘quarter jansky sample’ of extragalactic sources, defined at 408 MHz

1986 ◽  
Vol 119 ◽  
pp. 193-194
Author(s):  
Gopal Krishna ◽  
L. Saripalli ◽  
D.J. Saikia ◽  
R.A. Sramek
Keyword(s):  
Radio Emission ◽  
Flux Density ◽  
Density Range ◽  
Complete Sample

For a complete sample of 42 sources, defined over a narrow flux density range around 0.25 Jy at 408 MHz, properties related to size and nuclear radio emission are discussed and compared with the 3CR sample.

scholarly journals The Intergalactic Medium

1982 ◽  
Vol 97 ◽  
pp. 453-459
Author(s):  
A. C. Fabian ◽  
A. K. Kembhavi
Keyword(s):  
Radio Emission ◽  
Intergalactic Medium ◽  
Radio Sources ◽  
Clusters Of Galaxies ◽  
Intergalactic Gas ◽  
X Ray ◽  
Extended Radio ◽  
X Ray Background ◽  
Ngc 1275 ◽  
Intracluster Gas

The density of intergalactic gas may be an important parameter in the formation of extended radio sources. It may range from ∼ 0.1 particle cm−3 in the centres of some rich clusters of galaxies down to 10−8cm−3 or less in intercluster space. The possible influence of the intracluster gas surrounding NGC 1275 on its radio emission is discussed, and the possibility that a significant fraction of the X-ray background is due to a hot intergalactic medium is explored in some detail.

scholarly journals Radio Source Environments at Redshifts > 0.5

1996 ◽  
Vol 175 ◽  
pp. 321-322
Author(s):  
M. Lacy ◽  
S. Rawlings ◽  
M. Wold ◽  
A. Bunker ◽  
K.M. Blundell ◽  
...  
Keyword(s):  
Radio Source ◽  
High Redshift ◽  
Elliptical Galaxies ◽  
Radio Sources ◽  
Powerful Radio ◽  
Host Galaxies ◽  
Local Universe ◽  
Wide Range ◽  
Age Of The Universe ◽  
The Universe

The most powerful radio sources in the local Universe are found in giant elliptical galaxies. Looking back to a redshift of 0.5 (≈ half the age of the Universe for ω = 1), we see that these host galaxies are increasingly found in moderately rich clusters. This fact gives us hope that radio sources can be used as tracers of high density environments at high redshift. By exploiting radio source samples selected over a wide range in luminosity (Blundell et al., these proceedings), we will also be able to test whether the luminosities of radio sources are correlated with their environments.

Sign in / Sign up

Export Citation Format

Share Document