QSQs and Radio Galaxies - their Spectra and Time Variations at Radio Frequencies

1972 ◽  
Vol 44 ◽  
pp. 232-248
Author(s):  
Beverley J. Harris
Keyword(s):  
Radio Galaxies ◽  
Radio Sources ◽  
Optical Identification ◽  
High Frequencies ◽  
Compact Component ◽  
Sky Survey ◽  
Time Variations ◽  
Radio Frequencies ◽  
Luminous Objects ◽  
Interplanetary Scintillations

Accurate relative spectra for 300 radio sources from the Parkes catalogue have been measured and a statistical study made of their relation to class of optical identification and to other radio properties. Individual spectra and their time variations have also been investigated.The results support the contention that radio sources for which no identification appears on the Palomar Sky Survey prints may be galaxies more luminous at radio frequencies than those which are identified. From a study of QSOs, radio galaxies and these blank field objects, it appears (a) that with increasing radio luminosity compact components are more often found, their presence being indicated by synchrotron self-absorption at low and high frequencies, by flat, variable spectra at high frequencies, and by interplanetary scintillations; and (b) that where no compact component contributes to the spectrum at high frequencies, many spectra steepen with increasing frequency, an effect which may be more marked for the more radio luminous objects.Detailed analyses of the time variations in the compact components of 22 variable sources are generally consistent with the adiabatically expanding, uniform sphere model of Shklovsky, Kellermann, van der Laan and others. The model was modified to include relativistic expansion according to the formulae given by Rees and Simon. The results suggest that these components have evolved within months or years, have linear dimension of 0.1 to 100 pc and magnetic fields of 1 to 10−4 G. Some spectra at frequencies above 5000 MHz suggest non-adiabatic expansion which may be the result of continued injection of energy into an expanding region.

scholarly journals The low-frequency properties of FR 0 radio galaxies

2019 ◽  
Vol 631 ◽  
pp. A176 ◽  
Author(s):  
A. Capetti ◽  
R. D. Baldi ◽  
M. Brienza ◽  
R. Morganti ◽  
G. Giovannini
Keyword(s):  
Large Population ◽  
Low Frequency ◽  
Radio Galaxies ◽  
Radio Spectrum ◽  
Radio Sources ◽  
High Frequencies ◽  
Sky Survey ◽  
5 Ghz ◽  
Frequency Properties ◽  
Extended Emission

Using the alternative data release of the TIFR GMRT Sky Survey (TGSS), we studied the low-frequency properties of FR 0 radio galaxies, the large population of compact radio sources associated with red massive early-type galaxies revealed by surveys at 1.4 GHz. We considered TGSS observations from FR0CAT, a sample formed by 104 FR 0s at z <  0.05: all but one of them are covered by the TGSS, and 43 of them are detected above a 5σ limit of 17.5 mJy. No extended emission has been detected around the FR 0s, corresponding to a luminosity limit of ≲4 × 1023 W Hz−1 over an area of 100 kpc × 100 kpc. All but eight FR 0s have a flat or inverted spectral shape (α <  0.5) between 150 MHz and 1.4 GHz: this spectral behavior confirms the general paucity of optically thin extended emission within the TGSS beam, as is expected for their compact 1.4 GHz morphology. Data at 5 GHz were used to build their radio spectra, which are also generally flat at higher frequencies. By focusing on a sub-sample of FR 0s with flux density > 50 mJy at 1.4 GHz, we found that ∼75% of them have a convex spectrum, but with a smaller curvature than the more powerful gigahertz peaked-spectrum sources (GPS). The typical FR 0s radio spectrum is better described by a gradual steepening toward high frequencies, rather than to a transition from an optically-thick to an optically-thin regime, possibly observed in only ∼15% of the sample.

scholarly journals Optical Identification Strategies for the Molonglo Cluster Survey

1997 ◽  
Vol 14 (3) ◽  
pp. 221-229 ◽  
Author(s):  
A. J. Haigh ◽  
J. G. Robertson ◽  
R. W. Hunstead
Keyword(s):  
Production Rate ◽  
Radio Galaxies ◽  
Radio Sources ◽  
Optical Identification ◽  
Strong Concentration ◽  
Sky Survey ◽  
Extended Sources ◽  
Abell Cluster ◽  
Absolute Magnitudes ◽  
Optical Identifications

AbstractWe describe a newly refined procedure for making optical identifications of radio sources in Abell cluster fields observed with the Molonglo Observatory Synthesis Telescope (MOST). The method is based on past experience but uses a range of new tools to improve the reliability and production rate of identification lists. The COSMOS/UKST Southern Sky Object Catalogue was used to make preliminary identifications which were then inspected visually with the assistance of computer generated overlays of the MOST images and the Digitized Sky Survey (DSS). The overlaid images were essential for securing identifications for the extended sources prevalent among nearby clusters.We find 21±1·5% of the radio sources are identified with galaxies and 4·6±0·7% with QSO candidates in a sample of 927 radio sources in 27 cluster fields. We make a preliminary attempt to separate cluster radio galaxies from interlopers on the basis of absolute magnitudes. A strong concentration of radio galaxies was found at projected distances less than 100 kpc from the cluster centres and a weaker concentration for projected distances of 100–500 kpc.

scholarly journals The optical identification of radio sources

1959 ◽  
Vol 9 ◽  
pp. 507-513
Author(s):  
D. W. Dewhirst
Keyword(s):  
Radio Sources ◽  
Astronomy Observatory ◽  
National Geographic Society ◽  
Optical Identification ◽  
National Geographic ◽  
Extensive Search ◽  
Sky Survey ◽  
A Minor ◽  
Minor Character

Previous attempts to identify any large proportion of the discrete sources discovered at meter wavelengths have met with small success. In the investigation briefly reported here an extensive search has been made on the original plates of the 48-inch Palomar—National Geographic Society Sky Survey, using the available published radio data, but more especially the as yet unpublished results of a survey between +50 and −10 degrees declination that has been made with the interferometer of the Mullard Radio Astronomy Observatory, Cambridge. This radio survey (3C) has been carried out at 159.5 Mc/s using the aerial array of the 2C survey [1] in modified form. An account of the observation and reduction of this recent survey is given by other speakers in the Symposium. The area of sky covered by the 3C survey, and the criteria for the selection and classification of the sources, are likely to undergo small extensions and modifications before the final catalog is ready for publication, but these modifications will be of a minor character and will not alter the general conclusions of the present paper.

scholarly journals Radio-optical Identification of Very-Steep Spectrum Radio Sources from the UTR-2 Catalogue

2002 ◽  
Vol 199 ◽  
pp. 217-218 ◽  
Author(s):  
H. Andernach ◽  
O.V. Verkhodanov ◽  
N.V. Verkhodanova
Keyword(s):  
Radio Source ◽  
High Redshift ◽  
Radio Galaxies ◽  
Image Databases ◽  
Radio Continuum ◽  
Radio Sources ◽  
Optical Identification ◽  
X Ray ◽  
Spectrum Radio

We used radio source catalogues accessible from the CATS database to establish radio continuum spectra for decametric radio sources in the UTR-2 catalogue. In an attempt to find further candidates for high-redshift radio galaxies, we searched the FIRST and NVSS surveys for counterparts of a sample of UTR sources with ultra-steep radio spectra (USS, α ≤ −1.2, S ∼ vα). We derived accurate positions and sizes for 23 of these USS sources. The search for optical counterparts from the APM (object) and DSS (image) databases, as well as infrared and X—ray identifications of these UTR sources are in progress.

scholarly journals Structure of 194 Southern Declination Radio Sources from Interplanetary Scintillations

1974 ◽  
Vol 27 (1) ◽  
pp. 121 ◽  
Author(s):  
SM Bhandari ◽  
S Ananthakrishnan ◽  
A Pramesh Rao
Keyword(s):  
Spectral Index ◽  
Angular Size ◽  
Radio Sources ◽  
Interplanetary Scintillation ◽  
Blank Field ◽  
Sky Survey ◽  
Interplanetary Scintillations

Interplanetary scintillation observations of 194 southern declination radio sources have been made at 327 MHz. The angular size and the fraction of the flux present in the scintillating component have been estimated. More than half of the observed sources scintillate and contain ;;;'10% of their flux in angular size smaller than 0"�5. About 75 % of the quasars and '" 50 % of the galaxies and the blank field objects scintillate. For quasars the spectral index seems to be correlated with the strength of scintillation; most of the flat spectrum quasars are strong scintillators and are unresolved. The scintillating properties of blank field objects are consistent with Bolton's hypothesis that most of these are galaxies beyond the plate limit of the Sky Survey.

Radio Observations of Clusters of Galaxies

1967 ◽  
Vol 1 (1) ◽  
pp. 24-24
Author(s):  
B. Y. Mills ◽  
R. R. Shobbrook
Keyword(s):  
High Resolution ◽  
Luminosity Function ◽  
Radio Galaxies ◽  
Detailed Examination ◽  
Statistical Information ◽  
Radio Sources ◽  
Clusters Of Galaxies ◽  
Radio Observations ◽  
Radio Frequencies

High resolution studies of clusters of galaxies at radio frequencies may contribute substantially to our knowledge of the properties of radio galaxies, their evolution and their luminosity function. A considerable amount of statistical information is already available on the correspondence of radio sources and clusters; the present investigation is aimed rather at a detailed examination of the sources and their identification with actual galaxies or other objects.

scholarly journals Catalogue with visual morphological classification of 32,616 radio galaxies with optical hosts

2019 ◽  
Vol 15 (S356) ◽  
pp. 361-363
Author(s):  
Natalia Żywucka ◽  
Dorota Koziel-Wierzbowska ◽  
Arti Goyal
Keyword(s):  
Signal To Noise Ratio ◽  
Radio Galaxies ◽  
Sloan Digital Sky Survey ◽  
Radio Sources ◽  
Type I ◽  
Host Galaxies ◽  
Contour Maps ◽  
Narrow Angle ◽  
Sky Survey

AbstractWe present the catalogue of Radio sources associated with Optical Galaxies and having Unresolved or Extended morphologies I (ROGUE I). It was generated by cross-matching galaxies from the Sloan Digital Sky Survey Data Release 7 (SDSS DR 7) as well as radio sources from the First Images of Radio Sky at Twenty Centimetre (FIRST) and the National Radio Astronomical Observatory VLA Sky Survey (NVSS) catalogues. We created the largest handmade catalogue of visually classified radio objects and associated with them optical host galaxies, containing 32,616 galaxies with a FIRST core within 3 arcsec of the optical position. All listed objects possess the good quality SDSS DR 7 spectra with the signal-to-noise ratio > 10 and spectroscopic redshifts up to z = 0.6. The radio morphology classification was performed by a visual examination of the FIRST and the NVSS contour maps overlaid on a DSS image, while an optical morphology classification was based on the 120 arcsec snapshot images from SDSS DR 7.The majority of radio galaxies in ROGUE I, i.e. ∼ 93%, are unresolved (compact or elongated), while the rest of them exhibit extended morphologies, such as Fanaroff-Riley (FR) type I, II, and hybrid, wide-angle tail, narrow-angle tail, head-tail sources, and sources with intermittent or reoriented jet activity, i.e. double–double, X–shaped, and Z–shaped. Most of FR IIs have low radio luminosities, comparable to the luminosities of FR Is. Moreover, due to visual check of all radio maps and optical images, we were able to discover or reclassify a number of radio objects as giant, double–double, X–shaped, and Z–shaped radio galaxies. The presented sample can serve as a database for training automatic methods of identification and classification of optical and radio galaxies.

scholarly journals The LOFAR view of intergalactic magnetic fields with giant radio galaxies

2020 ◽  
Vol 638 ◽  
pp. A48 ◽  
Author(s):  
C. Stuardi ◽  
S. P. O’Sullivan ◽  
A. Bonafede ◽  
M. Brüggen ◽  
P. Dabhade ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Faraday Rotation ◽  
Detection Rate ◽  
Intergalactic Medium ◽  
Low Frequency ◽  
Radio Galaxies ◽  
Radio Sources ◽  
Weak Magnetic Fields ◽  
Polarization Study ◽  
Sky Survey

Context. Giant radio galaxies (GRGs) are physically large radio sources that extend well beyond their host galaxy environment. Their polarization properties are affected by the poorly constrained magnetic field that permeates the intergalactic medium on megaparsec scales. A low frequency (< 200 MHz) polarization study of this class of radio sources is now possible with LOFAR. Aims. Here we investigate the polarization properties and Faraday rotation measure (RM) of a catalog of GRGs detected in the LOFAR Two-meter Sky Survey. This is the first low frequency polarization study of a large sample of radio galaxies that were selected on their physical size. We explore the magneto-ionic properties of their under-dense environment and probe intergalactic magnetic fields using the Faraday rotation properties of their radio lobes. LOFAR is a key instrument for this kind of analysis because it can probe small amounts of Faraday dispersion (< 1 rad m−2), which are associated with weak magnetic fields and low thermal gas densities. Methods. We used RM synthesis in the 120−168 MHz band to search for polarized emission and to derive the RM and fractional polarization of each detected source component. We study the depolarization between 1.4 GHz and 144 MHz using images from the NRAO VLA Sky Survey. We investigate the correlation of the detection rate, the RM difference between the lobes, and the depolarization with different parameters as follows: the angular and linear size of the sources and the projected distance from the closest foreground galaxy cluster. In our sample, we also included 3C 236, which is one of the largest radio galaxies known. Results. From a sample of 240 GRGs, we detected 37 sources in polarization, all of which have a total flux density above 56 mJy. We detected significant RM differences between the lobes, which would be inaccessible at gigahertz frequencies, with a median value of ∼1 rad m−2. The fractional polarization of the detected GRGs at 1.4 GHz and 144 MHz is consistent with a small amount of Faraday depolarization (a Faraday dispersion < 0.3 rad m−2). Our analysis shows that the lobes are expanding into a low-density (< 10−5 cm−3) local environment that is permeated by weak magnetic fields (< 0.1 μG) with fluctuations on scales of 3−25 kpc. The presence of foreground galaxy clusters appears to influence the polarization detection rate up to 2R500. In general, this work demonstrates the ability of LOFAR to quantify the rarefied environments in which these GRGs exist and highlights them as an excellent statistical sample to use as high precision probes of magnetic fields in the intergalactic medium and the Milky Way.

scholarly journals Relations Between Radio and Optical Properties of Radio Sources - Radio Astronomer's Point of View

1977 ◽  
Vol 74 ◽  
pp. 237-243
Author(s):  
J. M. Riley ◽  
C. J. Jenkins
Keyword(s):  
Optical Properties ◽  
Radio Galaxies ◽  
Point Of View ◽  
Radio Sources ◽  
Optical Identification ◽  
Complete Sample ◽  
Radio Structure ◽  
Quasars And Radio Galaxies

One particular aspect of the relations between the radio and optical properties of radio sources has been examined for a complete sample of 3CR sources, namely the relation between the radio structure of a source and its optical identification. Possible differences between the radio structures of quasars and radio galaxies are investigated, and the data provide clues as to the optical nature of the unidentified sources.

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