scholarly journals Remnant Radio Galaxy Candidates of Small Angular Sizes

Galaxies ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 121
Author(s):  
Veeresh Singh ◽  
Sushant Dutta ◽  
Yogesh Wadadekar ◽  
C. H. Ishwara-Chandra
Keyword(s):  
Radio Galaxy ◽  
Spectral Characteristics ◽  
Angular Size ◽  
Active Phase ◽  
Radio Galaxies ◽  
Upper Limit ◽  
Active Core ◽  
Morphological Criteria ◽  
Frequency Regime ◽  
Jet Power

Remnant radio galaxies (RRGs), characterized by the cessation of AGN activity, represent a short-lived last phase of radio galaxy’s life-cycle. Hitherto, searches for RRGs, mainly based on the morphological criteria, have identified large angular size sources resulting into a bias towards the remnants of powerful FR-II radio galaxies. In this study we make the first attempt to perform a systematic search for RRGs of small angular sizes (<30′′) in the XMM−LSS field. By using spectral curvature criterion we discover 48 remnant candidates exhibiting strong spectral curvature i.e.,   α150MHz325MHz−α325MHz1.4GHz≥ 0.5. Spectral characteristics at higher frequency regime (>1.4 GHz) indicate that some of our remnant candidates can depict recurrent AGN activity with an active core. We place an upper limit on the remnant fraction (frem) to be 3.9%, which increases to 5.4% if flux cutoff limit of S150MHz≥ 10 mJy is considered. Our study unveils, hitherto unexplored, a new population of small-size (<200 kpc) remnant candidates that are often found to reside in less dense environments and at higher redshifts (z) > 1.0. We speculate that a relatively shorter active phase and/or low jet power can be plausible reasons for the small size of remnant candidates.

scholarly journals The faint radio source population at 15.7 GHz – IV. The dominance of core emission in faint radio galaxies

2020 ◽  
Vol 493 (2) ◽  
pp. 2841-2853
Author(s):  
I H Whittam ◽  
D A Green ◽  
M J Jarvis ◽  
J M Riley
Keyword(s):  
High Frequency ◽  
Angular Size ◽  
Radio Galaxies ◽  
Mixed Population ◽  
Source Population ◽  
Large Array ◽  
High Excitation ◽  
Complete Sample ◽  
Very Large Array ◽  
Upper Limit

ABSTRACT We present 15-GHz Karl G. Jansky Very Large Array observations of a complete sample of radio galaxies selected at 15.7 GHz from the Tenth Cambridge (10C) survey. 67 out of the 95 sources (71 per cent) are unresolved in the new observations and lower frequency radio observations, placing an upper limit on their angular size of ∼2 arcsec. Thus, compact radio galaxies, or radio galaxies with very faint jets, are the dominant population in the 10C survey. This provides support for the suggestion in our previous work that low-luminosity ($L\lt 10^{25} \, \textrm{W~Hz}^{-1}$) radio galaxies are core dominated, although higher resolution observations are required to confirm this directly. The 10C sample of compact, high-frequency selected radio galaxies is a mixture of high-excitation and low-excitation radio galaxies and displays a range of radio spectral shapes, demonstrating that they are a mixed population of objects.

scholarly journals The Origin and Evolution of Giant Radio Galaxies

2022 ◽  
Vol 8 ◽  
Author(s):  
David Garofalo
Keyword(s):  
Black Hole ◽  
Active Galactic Nuclei ◽  
Spiral Galaxies ◽  
Radio Galaxy ◽  
Galactic Nuclei ◽  
Radio Galaxies ◽  
High Excitation ◽  
Origin And Evolution ◽  
Black Hole Spin ◽  
Upper Limit

Giant radio galaxies are arguably the least understood of jetted active galactic nuclei (AGN). We propose that radio galaxies are the product of large mergers that do not involve radio galaxies or radio quasars, such as in merging spiral galaxies, while giant radio galaxies emerge from a merger involving a parent that in the not-too-distant past harbored a radio galaxy. Predictions following from this are an upper limit to the number fraction of giant radio galaxies to radio galaxies, lower average redshift for giant radio galaxies, a higher incidence of high excitation for giant radio galaxies compared with radio galaxies, and lower average prograde black hole spin values for giant radio galaxies compared to radio galaxies and to bright radio quiet quasars.

scholarly journals Discovery of 178 Giant Radio Galaxies in 1059 deg2 of the Rapid ASKAP Continuum Survey at 888 MHz

Galaxies ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 99
Author(s):  
Heinz Andernach ◽  
Eric F. Jiménez-Andrade ◽  
Anthony G. Willis
Keyword(s):  
Radio Galaxy ◽  
Angular Size ◽  
Radio Galaxies ◽  
Infrared Images ◽  
Host Galaxies ◽  
Photometric Redshifts ◽  
Dark Energy Survey ◽  
Optical Images ◽  
Extended Radio ◽  
Energy Survey

We report the results of a visual inspection of images of the Rapid ASKAP Continuum Survey (RACS) in search of extended radio galaxies (ERG) that reach or exceed linear sizes on the order of one Megaparsec. We searched a contiguous area of 1059 deg2 from RAJ = 20h20m to 06h20m, and −50∘<DecJ<−40∘, which is covered by deep multi-band optical images of the Dark Energy Survey (DES) and in which previously only three ERGs larger than 1 Mpc had been reported. For over 1800 radio galaxy candidates inspected, our search in optical and infrared images resulted in hosts for 1440 ERG, for which spectroscopic and photometric redshifts from various references were used to convert their largest angular size (LAS) to projected linear size (LLS). This resulted in 178 newly discovered giant radio sources (GRS) with LLS >1 Mpc, of which 18 exceed 2 Mpc and the largest one is 3.4 Mpc. Their redshifts range from 0.02 to ∼2.0, but only 10 of the 178 new GRS have spectroscopic redshifts. For the 146 host galaxies, the median r-band magnitude and redshift are 20.9 and 0.64, while for the 32 quasars or candidates these are 19.7 and 0.75. Merging the six most recent large compilations of GRS results in 458 GRS larger than 1 Mpc, so we were able to increase this number by ∼39% to 636.

scholarly journals Observations of Southern Radio Galaxies at 1415 MHz

1992 ◽  
Vol 45 (6) ◽  
pp. 797 ◽  
Author(s):  
PA Jones
Keyword(s):  
Spectral Index ◽  
Angular Size ◽  
Radio Galaxies ◽  
Beam Size

The structures of 23 strong radio galaxies, all with angular size larger than 3 arcmin, have been observed with the Fleurs Synthesis Telescope (FST) at 1415 MHz with a resolution of 22 arcsec. Spectral index differences within the sources were investigated by omparing 843 MHz images made with the Molonglo Observatory Synthesis Telescope (MOST) with FST images convolved to the same beam-size of 44 arcsec.

scholarly journals Radio Spectra and Particle Ages of the Head-Tail Radio Galaxy NGC1265

1996 ◽  
Vol 175 ◽  
pp. 347-348
Author(s):  
L. Feretti ◽  
G. Giovannini ◽  
U. Klein ◽  
K.-H. Mack ◽  
L.G. Sijbring
Keyword(s):  
Magnetic Field ◽  
Radio Galaxy ◽  
Low Frequency ◽  
Radio Galaxies ◽  
Field Structure ◽  
Magnetic Field Structure ◽  
Linearly Polarized ◽  
Faraday Effects ◽  
Perseus Cluster ◽  
Comprehensive Study

We have performed sensitive observations of three classical head-tail radio galaxies at λ11.1, 6.3, and 2.8 cm using the Effelsberg 100-m telescope (Zech, 1994). Complete maps of the sources 3C129, NGC1265, and 3C465 were obtained, including the distributions of the linearly polarized intensity. Together with the low-frequency interferometric maps these allow a comprehensive study of their radio spectra and, based on models of particle losses, the derivations of particle ages across these sources. The highest frequency involved allows an unambiguous derivation of the projected magnetic field structure, unimpeded by Faraday effects. Here we focus on NGC1265, which is located in the Perseus Cluster.

scholarly journals NGC 3894: a young radio galaxy seen by Fermi-LAT

2020 ◽  
Vol 635 ◽  
pp. A185 ◽  
Author(s):  
G. Principe ◽  
G. Migliori ◽  
T. J. Johnson ◽  
F. D’Ammando ◽  
M. Giroletti ◽  
...  
Keyword(s):  
Radio Galaxy ◽  
Radio Galaxies ◽  
High Energy ◽  
Apparent Velocity ◽  
Large Area ◽  
Long Baseline ◽  
Full Period ◽  
Very Long Baseline Array ◽  
High Energy Emission ◽  
First Time

Context. According to radiative models, radio galaxies may produce γ-ray emission from the first stages of their evolution. However, very few such galaxies have been detected by the Fermi Large Area Telescope (LAT) so far. Aims. NGC 3894 is a nearby (z = 0.0108) object that belongs to the class of compact symmetric objects (CSOs, i.e., the most compact and youngest radio galaxies), which is associated with a γ-ray counterpart in the Fourth Fermi-LAT source catalog. Here we present a study of the source in the γ-ray and radio bands aimed at investigating its high-energy emission and assess its young nature. Methods. We analyzed 10.8 years of Fermi-LAT data between 100 MeV and 300 GeV and determined the spectral and variability characteristics of the source. Multi-epoch very long baseline array (VLBA) observations between 5 and 15 GHz over a period of 35years were used to study the radio morphology of NGC 3894 and its evolution. Results. NGC 3894 is detected in γ-rays with a significance >9σ over the full period, and no significant variability has been observed in the γ-ray flux on a yearly time-scale. The spectrum is modeled with a flat power law (Γ = 2.0 ± 0.1) and a flux on the order of 2.2 × 10−9 ph cm−2 s−1. For the first time, the VLBA data allow us to constrain with high precision the apparent velocity of the jet and counter-jet side to be βapp, NW = 0.132 ± 0.004 and βapp, SE = 0.065 ± 0.003, respectively. Conclusions. Fermi-LAT and VLBA results favor the youth scenario for the inner structure of this object, with an estimated dynamical age of 59 ± 5 years. The estimated range of viewing angle (10° < θ <  21°) does not exclude a possible jet-like origin of the γ-ray emission.

scholarly journals The morphological classification of distant radio galaxies explored with three-dimensional simulations

2019 ◽  
Vol 490 (1) ◽  
pp. 1363-1382 ◽  
Author(s):  
Michael D Smith ◽  
Justin Donohoe
Keyword(s):  
Radio Galaxy ◽  
Three Dimensional ◽  
Radio Galaxies ◽  
Morphological Classification ◽  
Helical Structures ◽  
Radio Jets ◽  
Source Type ◽  
Radio Lobe ◽  
Three Dimensional Simulations

ABSTRACT We explore the observational implications of a large systematic study of high-resolution three-dimensional simulations of radio galaxies driven by supersonic jets. For this fiducial study, we employ non-relativistic hydrodynamic adiabatic flows from nozzles into a constant pressure-matched environment. Synchrotron emissivity is approximated via the thermal pressure of injected material. We find that the morphological classification of a simulated radio galaxy depends significantly on several factors with increasing distance (i.e. decreasing observed resolution) and decreasing orientation often causing reclassification from FR II (limb-brightened) to FR I (limb-darkened) type. We introduce the Lobe or Limb Brightening Index (LBI) to measure the radio lobe type more precisely. The jet density also has an influence as expected with lower density leading to broader and bridged lobe morphologies as well as brighter radio jets. Hence, relating observed source type to the intrinsic jet dynamics is not straightforward. Precession of the jet direction may also be responsible for wide relaxed sources with lower LBI and FR class as well as for X-shaped and double–double structures. Helical structures are not generated because the precession is usually too slow. We conclude that distant radio galaxies could appear systematically more limb darkened due to merger-related redirection and precession as well as due to the resolution limitation.

scholarly journals Near Infrared and Radio Observations of Distant Galaxies

1983 ◽  
Vol 104 ◽  
pp. 85-86
Author(s):  
R. A. Laing ◽  
F. N. Owen ◽  
J. J. Puschell
Keyword(s):  
Near Infrared ◽  
Angular Size ◽  
Radio Galaxies ◽  
Radio Observations ◽  
Chance Coincidence ◽  
Distant Galaxies ◽  
Upper Limits

This paper is concerned with the distant radio galaxies in a sample of bright sources selected at 178 MHz by Laing, Riley & Longair (1982). This sample is 96% complete for sources with θ < 10′ and the bias of the 3CR catalogue against sources of large angular size has also been reduced. Deep optical searches have located many candidate identifications, but the probability of a chance coincidence with an unrelated object is appreciable, especially in the faintest cases, unless the area to be searched is small. We have therefore mapped the sources with candidate identifications having V > 20, using the VLA at a wavelength of 6 cm (Laing, Owen & Puschell, in preparation), in order to search for radio cores. We have so far located cores in 16/23 sources and set 5σ upper limits of 0.6 mJy for the remainder. None of the cores had been detected previously. In all cases, the cores coincide with optical objects, although one source (3C 340) had been misidentified. Several ambiguities have now been resolved.

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