scholarly journals Radio Galaxies and Quasars as Cosmological Probes

1996 ◽  
Vol 168 ◽  
pp. 71-78
Author(s):  
Ashok K. Singal
Keyword(s):  
Angular Size ◽  
Radio Galaxies ◽  
Radio Sources ◽  
Powerful Radio ◽  
Extragalactic Radio Sources ◽  
Relativistic Beaming ◽  
Extended Radio ◽  
Statistical Sense ◽  
Cosmological Tests ◽  
The Universe

Various techniques and methods that have been developed for using extragalactic radio sources as cosmological probes of the universe are listed. The discussion is mainly confined to the cosmological tests employing extended radio sizes of powerful radio galaxies and quasars as standard metric rods (in a statistical sense) to figure out the geometry of the universe. Some comments are made on the recent use of the milliarcsec scale sizes of compact radio sources for angular size–redshift tests. It is further pointed out that the estimates of clustering for quasars selected at centimetre wavelengths could be seriously affected by the relativistic beaming.

Tables of physical and morphological properties of nearby extended radio galaxies

2021 ◽  
pp. 75-89
Author(s):  
R. R. Andreasyan ◽  
H. V. Abrahamyan
Keyword(s):  
Radio Galaxies ◽  
Elliptical Galaxies ◽  
Morphological Data ◽  
Morphological Properties ◽  
Radio Sources ◽  
Extragalactic Radio Sources ◽  
Extended Radio

It is brought the physical and morphological data of 267 nearby radio galaxies identified with elliptical galaxies brighter than 18th magnitude (sample 1) and for 280 extragalactic radio sources with known position angles between the integrated intrinsic radio polarization and radio axes (sample 2).

scholarly journals Spatial Correlation Functions of Bright Radio Galaxies

1988 ◽  
Vol 130 ◽  
pp. 580-580 ◽  
Author(s):  
You-yuan Zhou ◽  
Yi-peng Jing
Keyword(s):  
Correlation Function ◽  
Spatial Correlation ◽  
Correlation Functions ◽  
Radio Galaxies ◽  
Radio Sources ◽  
Spatial Correlation Function ◽  
Extragalactic Radio Sources ◽  
Large Separation ◽  
The Universe

Because of their large separation bright radio galaxies characterize the structure of the universe on the scales of clusters and superclusters. In order to calculate the spatial correlation function we choose radio galaxies in radio surveys, for which the redshift values have been measured. One is from Bright Radio Sources at 178 MHz (Liang, Riley and Longair 1983), and another is from All-Sky Catalogue of Bright Extragalactic Radio Sources at 2.7 GHz (Wall and Peacock 1985).

scholarly journals Weathering the Largest Storms in the Universe: Understanding environmental effects on extended radio emission in clusters

2021 ◽  
Author(s):  
◽  
Siamak Dehghan
Keyword(s):  
Structure Analysis ◽  
Large Scale ◽  
Radio Galaxy ◽  
Radio Galaxies ◽  
Radio Sources ◽  
Radio Luminosity ◽  
Star Forming ◽  
Extended Radio ◽  
The Universe

<p>This thesis presents an investigation of the habitat of extended radio sources, and the way in which the generation and properties of these radio sources are affected by environmental factors. We begin with a detailed structure analysis of the 0.3 deg² area of the MUSYC-ACES field, generated by applying a density-based clustering method, known as DBSCAN, to our spectroscopic and photometric samples of the field. As a result, we identify 62 over-dense regions across the field. Based on the properties of the detected structures, we classify 13 as clusters, of which 90% are associated with diffuse soft-band X-ray emission. This provides a strong and independent confirmation that both the clustering and classification methodologies are reliable for use in investigation of the environment of the radio sources in the Chandra Deep Field South (CDFS).  Using an interpolation-based method followed by a new calibration technique of using clusters of similar mass as standard candles, we are able to estimate the local environmental richness for a desired region. This methodology is applied to a sample of AGNs and star forming galaxies in the CDFS to probe whether or not the radio luminosity of the different radio sources is correlated to their environments. As a result, we do not find a significant correlation between the radio luminosity and the environment of star-forming galaxies and radio-quiet AGNs, however, a weak positive dependency is spotted for radio-loud AGNs. This may indicate that over-populated environments trigger or enhance the radio activity processes in the AGNs. We find that star-forming galaxies, unlike radio-loud AGNs, tend to avoid overpopulated environments especially at low redshifts. However, radio-loud AGN are found in both poor and rich environments. As a result, we find neither of these radio sources suitable for tracing the over-dense regions of the Universe, unlike tailed radio galaxies.  It is believed that tailed radio galaxies reside in the dense environments of clusters and groups, and therefore, may be the signatures of overdensities in large-scale structure. To evaluate the idea of using tailed radio galaxies as tracers of dense environments, a systematic study of these sources as a function of density is required. For this reason and by using the 1.4 GHz Australia Telescope Large Area Survey (ATLAS) data, we examined over four deg² area of the ATLAS-CDFS field, which includes the entire CDFS. We present a catalogue of 56 non-linear, extended, and low surface brightness sources including 45 tailed radio galaxies, two relic candidates, and a possible radio halo. We report the detection of the most distant tailed radio galaxy to date, at a redshift of 2.1688. In addition, despite the lack of deep spectroscopic data in the ATLAS field, we find two of the detected tailed radio galaxies are associated with clusters. We find three Head-Tail galaxy candidates in the CDFS field, all of which are located at high redshifts, where the magnitude constraint of our redshift sample prevents any structure detection.  One of the primary objectives of this research is to investigate the association between the morphology of tailed radio galaxies and the physical characteristics of the surrounding environment. In order to understand the role of the variety of factors that influence the radio morphology, we constructed a simple model that generates the overall radio structure of the sources in different habitats. We report the results of the simulation of the wide-angle tail radio galaxy PKS J0334-3900, which shows that both the gravitation interactions and a cluster wind are required to generate the observed radio tails. As a result, we find the morphology of the tailed radio galaxies as an invaluable tool to probe environmental characteristics.  In a supplementary study, we investigate the role of cluster dynamics on generation and alternation of extended radio sources. We present a comprehensive structure and sub-structure analysis of the Abell 3266 galaxy cluster. Based on the results of the sub-structure test, position and orientation of a radio relic candidate, and morphology of a prominent tailed radio galaxy in the cluster, we propose an ongoing merger scenario for this chaotic cluster environment. Furthermore, we verify our theory by an N-body simulation of a pre-merger cluster and an in-falling group. The results of the simulation supports our merger scenario by explaining both the orientation of the radio relic and the observed morphology of the tailed radio galaxy.  While there is a weak correlation between the luminosity of radio-loud AGNs and environmental density, tailed radio galaxies make superior probes of over-dense regions. Thus, overall we find tailed radio galaxies can be used to trace overdensities out to z ~ 2 and probe the details of the environments in which they are found.</p>

scholarly journals Weathering the Largest Storms in the Universe: Understanding environmental effects on extended radio emission in clusters

2021 ◽  
Author(s):  
◽  
Siamak Dehghan
Keyword(s):  
Structure Analysis ◽  
Large Scale ◽  
Radio Galaxy ◽  
Radio Galaxies ◽  
Radio Sources ◽  
Radio Luminosity ◽  
Star Forming ◽  
Extended Radio ◽  
The Universe

<p>This thesis presents an investigation of the habitat of extended radio sources, and the way in which the generation and properties of these radio sources are affected by environmental factors. We begin with a detailed structure analysis of the 0.3 deg² area of the MUSYC-ACES field, generated by applying a density-based clustering method, known as DBSCAN, to our spectroscopic and photometric samples of the field. As a result, we identify 62 over-dense regions across the field. Based on the properties of the detected structures, we classify 13 as clusters, of which 90% are associated with diffuse soft-band X-ray emission. This provides a strong and independent confirmation that both the clustering and classification methodologies are reliable for use in investigation of the environment of the radio sources in the Chandra Deep Field South (CDFS).  Using an interpolation-based method followed by a new calibration technique of using clusters of similar mass as standard candles, we are able to estimate the local environmental richness for a desired region. This methodology is applied to a sample of AGNs and star forming galaxies in the CDFS to probe whether or not the radio luminosity of the different radio sources is correlated to their environments. As a result, we do not find a significant correlation between the radio luminosity and the environment of star-forming galaxies and radio-quiet AGNs, however, a weak positive dependency is spotted for radio-loud AGNs. This may indicate that over-populated environments trigger or enhance the radio activity processes in the AGNs. We find that star-forming galaxies, unlike radio-loud AGNs, tend to avoid overpopulated environments especially at low redshifts. However, radio-loud AGN are found in both poor and rich environments. As a result, we find neither of these radio sources suitable for tracing the over-dense regions of the Universe, unlike tailed radio galaxies.  It is believed that tailed radio galaxies reside in the dense environments of clusters and groups, and therefore, may be the signatures of overdensities in large-scale structure. To evaluate the idea of using tailed radio galaxies as tracers of dense environments, a systematic study of these sources as a function of density is required. For this reason and by using the 1.4 GHz Australia Telescope Large Area Survey (ATLAS) data, we examined over four deg² area of the ATLAS-CDFS field, which includes the entire CDFS. We present a catalogue of 56 non-linear, extended, and low surface brightness sources including 45 tailed radio galaxies, two relic candidates, and a possible radio halo. We report the detection of the most distant tailed radio galaxy to date, at a redshift of 2.1688. In addition, despite the lack of deep spectroscopic data in the ATLAS field, we find two of the detected tailed radio galaxies are associated with clusters. We find three Head-Tail galaxy candidates in the CDFS field, all of which are located at high redshifts, where the magnitude constraint of our redshift sample prevents any structure detection.  One of the primary objectives of this research is to investigate the association between the morphology of tailed radio galaxies and the physical characteristics of the surrounding environment. In order to understand the role of the variety of factors that influence the radio morphology, we constructed a simple model that generates the overall radio structure of the sources in different habitats. We report the results of the simulation of the wide-angle tail radio galaxy PKS J0334-3900, which shows that both the gravitation interactions and a cluster wind are required to generate the observed radio tails. As a result, we find the morphology of the tailed radio galaxies as an invaluable tool to probe environmental characteristics.  In a supplementary study, we investigate the role of cluster dynamics on generation and alternation of extended radio sources. We present a comprehensive structure and sub-structure analysis of the Abell 3266 galaxy cluster. Based on the results of the sub-structure test, position and orientation of a radio relic candidate, and morphology of a prominent tailed radio galaxy in the cluster, we propose an ongoing merger scenario for this chaotic cluster environment. Furthermore, we verify our theory by an N-body simulation of a pre-merger cluster and an in-falling group. The results of the simulation supports our merger scenario by explaining both the orientation of the radio relic and the observed morphology of the tailed radio galaxy.  While there is a weak correlation between the luminosity of radio-loud AGNs and environmental density, tailed radio galaxies make superior probes of over-dense regions. Thus, overall we find tailed radio galaxies can be used to trace overdensities out to z ~ 2 and probe the details of the environments in which they are found.</p>

COMMENT ON "ANGULAR SIZE TEST ON THE EXPANSION OF THE UNIVERSE," BY M. LÓPEZ-CORREDOIRA

2011 ◽  
Vol 20 (06) ◽  
pp. 1167-1169 ◽  
Author(s):  
D. L. KHOKHLOV
Keyword(s):  
Angular Size ◽  
Radio Sources ◽  
Expansion Of The Universe ◽  
The Difference ◽  
The Universe

The results of the angular size test in the paper under comment are at variance with those for compact radio sources. The possible reason for the difference between the two results is discussed.

scholarly journals Relations Between the Optical and Radio Properties of Extragalactic Radio Sources

1977 ◽  
Vol 74 ◽  
pp. 223-235
Author(s):  
E. M. Burbidge
Keyword(s):  
Optical Properties ◽  
Physical Theory ◽  
Radio Sources ◽  
Intrinsic Properties ◽  
Extragalactic Radio Sources ◽  
Nonthermal Radiation ◽  
The Universe

Correlations between the radio and optical properties of radio sources have proved elusive and the main conclusion to be drawn from this is that there is a great variety of objects in the universe that emit nonthermal radiation, so that attempts to use these objects for cosmological purposes can be frustrated unless one can find some way of selecting objects that do have common intrinsic properties. Despite this, the search for relations and correlations is interesting quite apart from cosmology, because such correlations should provide a groundwork for a physical theory or theories of what is really happening in sources of nonthermal radiation.

Optical Observations of Extragalactic Radio Sources

1967 ◽  
Vol 1 (1) ◽  
pp. 23-23
Author(s):  
B. E. Westerlund ◽  
J. V. Wall ◽  
N. R. Stokes
Keyword(s):  
Radio Galaxies ◽  
Optical Observations ◽  
Radio Sources ◽  
Extragalactic Radio Sources ◽  
Photometric Observations

Photometric observations on the UBV system have been made of a number of optically identified radio sources. The measurements are basically of two types: (1) offset photometry with the Siding Spring 40-inch reflector of objects identified as probable quasars or N galaxies, and (2) observations with the Siding Spring 24-inch reflector of radio galaxies brighter than V = 14m.0.

scholarly journals Expanding Quasars and the Expansion of the Universe

1988 ◽  
Vol 129 ◽  
pp. 23-24
Author(s):  
M. H. Cohen ◽  
P. D. Barthel ◽  
T. J. Pearson ◽  
J. A. Zensus
Keyword(s):  
Active Galactic Nuclei ◽  
Upper Bound ◽  
Proper Motion ◽  
Galactic Nuclei ◽  
Radio Sources ◽  
Extragalactic Radio Sources ◽  
Expansion Of The Universe ◽  
The Universe

The μ–z diagram (Figure 1) plots the observed internal proper motion μ versus redshift z for 32 extragalactic radio sources associated with active galactic nuclei. The observed points fall below an upper bound which decreases with redshift; there is a statistically significant anticorrelation between redshift and internal proper motion.

scholarly journals Cores in Extended Quasars

1984 ◽  
Vol 110 ◽  
pp. 39-40
Author(s):  
P. D. Barthel ◽  
G. K. Miley ◽  
R. T. Schilizzi ◽  
E. Preuss ◽  
T. J. Cornwell
Keyword(s):  
Radio Galaxies ◽  
Radio Sources ◽  
Extended Radio

The Nuclear Radio cores of several nearby extended radio galaxies (e.g. M87, 3C236) consist not only of optically thick (< 1 pc) components, but also of emission on somewhat larger scale. As extended radio sources associated with quasars have on average stronger and more luminous radio cores (see e.g. Miley, 1980, Ann. Rev. Astron. Astrophys. 18, 165), we have started a project to study the properties of these quasar cores.

Sign in / Sign up

Export Citation Format

Share Document