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.

Constraints on extragalactic-jet characteristics from lobe observations

1986 ◽  
Vol 64 (4) ◽  
pp. 378-380 ◽  
Author(s):  
Steven R. Spangler
Keyword(s):  
Hot Spot ◽  
Radio Galaxies ◽  
Large Array ◽  
Very Large Array ◽  
Upper Limits ◽  
Measured Speed ◽  
High Mach ◽  
Jet Characteristics ◽  
Double Radio Galaxies ◽  
Spot Motion

We discuss Very Large Array spectral and polarimetric observations of the lobes of luminous, double radio galaxies. These observations can provide information on the (typically undetected) jets responsible for the sources. Spectral steepening is usually observed in the lobes, with the radio spectral index increasing with distance from the hot spot. These data can be used to infer a "speed of separation" of the hot spot and lobe material. These speeds, typically 1.0 × 104–3.0 × 104 km/s, are in agreement with hydrocode models of jets, which interpret the measured speed of separation as a combination of hot-spot motion and backflow. Polarimetric observations indicate that in at least some sources, there is an undetectably small amount of internal Faraday rotation, indicating upper limits to the thermal-plasma density of a few times 10−5 cm−3 or less. These measurements are also in agreement with the numerical beam models, provided that the beam density is substantially less than that of the background medium. We conclude that the lobe observations indicate that these sources are powered by light, high-Mach-number beams.

scholarly journals Quasi-simultaneous Radio/X-Ray Observations of the Candidate Transitional Millisecond Pulsar 3FGL J1544.6−1125 during its Low-luminosity Accretion-disk State

2021 ◽  
Vol 923 (1) ◽  
pp. 3
Author(s):  
Amruta D. Jaodand ◽  
Adam T. Deller ◽  
Nina Gusinskaia ◽  
Jason W. T. Hessels ◽  
James C. A. Miller-Jones ◽  
...  
Keyword(s):  
Accretion Disk ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Large Array ◽  
Millisecond Pulsar ◽  
Very Large Array ◽  
X Ray ◽  
Upper Limit ◽  
5 Ghz ◽  
Variable Radio

Abstract 3FGL J1544.6−1125 is a candidate transitional millisecond pulsar (tMSP). Similar to the well-established tMSPs—PSR J1023+0038, IGR J18245−2452, and XSS J12270−4859—3FGL J1544.6−1125 shows γ-ray emission and discrete X-ray “low” and “high” modes during its low-luminosity accretion-disk state. Coordinated radio/X-ray observations of PSR J1023+0038 in its current low-luminosity accretion-disk state showed rapidly variable radio continuum emission—possibly originating from a compact, self-absorbed jet, the “propellering” of accretion material, and/or pulsar moding. 3FGL J1544.6−1125 is currently the only other (candidate) tMSP system in this state, and can be studied to see whether tMSPs are typically radio-loud compared to other neutron star binaries. In this work, we present a quasi-simultaneous Very Large Array and Swift radio/X-ray campaign on 3FGL J1544.6−1125. We detect 10 GHz radio emission varying in flux density from 47.7 ± 6.0 μJy down to ≲15 μJy (3σ upper limit) at four epochs spanning three weeks. At the brightest epoch, the radio luminosity is L 5 GHz = (2.17 ± 0.17) × 1027 erg s−1 for a quasi-simultaneous X-ray luminosity L 2–10 keV = (4.32 ± 0.23) × 1033 erg s−1 (for an assumed distance of 3.8 kpc). These luminosities are close to those of PSR J1023+0038, and the results strengthen the case that 3FGL J1544.6−1125 is a tMSP showing similar phenomenology to PSR J1023+0038.

scholarly journals The radio properties of high-excitation radio galaxies with intermediate radio powers

2020 ◽  
Vol 494 (2) ◽  
pp. 2053-2067
Author(s):  
J C S Pierce ◽  
C N Tadhunter ◽  
R Morganti
Keyword(s):  
High Resolution ◽  
Large Scale ◽  
High Sensitivity ◽  
Seyfert Galaxies ◽  
Radio Galaxies ◽  
Host Galaxy ◽  
High Excitation ◽  
Power Sources ◽  
Very Large Array ◽  
Extended Radio

ABSTRACT In the past decade, high-sensitivity radio surveys have revealed that the local radio active galactic nucleus population is dominated by moderate-to-low power sources with emission that is compact on galaxy scales. High-excitation radio galaxies (HERGs) with intermediate radio powers (22.5 < log (L1.4 GHz) < 25.0 W Hz−1) form an important sub-group of this population, since there is strong evidence that they also drive multiphase outflows on the scales of galaxy bulges. Here, we present high-resolution Very Large Array observations at 1.5, 4.5, and 7.5 GHz of a sample of 16 such HERGs in the local universe (z < 0.1), conducted in order to investigate the morphology, extent, and spectra of their radio emission in detail, down to sub-kpc scales. We find that the majority (56 per cent) have unresolved structures at the limiting angular resolution of the observations (∼0.3 arcsec). Although similar in the compactness of their radio structures, these sources have steep radio spectra and host galaxy properties that distinguish them from local low-excitation radio galaxies that are unresolved on similar scales. The remaining sources exhibit extended radio structures with projected diameters ∼1.4–19.0 kpc and a variety of morphologies: three double-lobed; two large-scale diffuse; one jetted and ‘S-shaped’; one undetermined. Only 19 per cent of the sample therefore exhibit the double-lobed/edge-brightened structures often associated with their counterparts at high and low radio powers: radio-powerful HERGs and Seyfert galaxies, respectively. Additional high-resolution observations are required to investigate this further, and to probe the ≲300 pc scales on which some Seyfert galaxies show extended structures.

scholarly journals Optical Morphologies of Millijansky Radio Galaxies Observed by theHubble Space Telescopeand in the Very Large Array FIRST Survey

2008 ◽  
Vol 179 (2) ◽  
pp. 306-318 ◽  
Author(s):  
J. Russell ◽  
R. E. Ryan, Jr. ◽  
S. H. Cohen ◽  
R. A. Windhorst ◽  
I. Waddington
Keyword(s):  
Radio Galaxies ◽  
Large Array ◽  
Very Large Array

scholarly journals Unveiling the nature of the unidentified gamma-ray sources: blazar counterparts at low radio frequencies

2013 ◽  
Vol 9 (S304) ◽  
pp. 95-95
Author(s):  
Francesco Massaro ◽  
R. D'Abrusco ◽  
M. Giroletti ◽  
A. Paggi ◽  
N. Masetti ◽  
...  
Keyword(s):  
Radio Emission ◽  
Gamma Ray ◽  
Low Frequency ◽  
Radio Galaxies ◽  
Large Array ◽  
New Approach ◽  
Very Large Array ◽  
Very Low Frequency ◽  
Sky Survey ◽  
Order Of Magnitude

AbstractAbout one third of the gamma-ray sources detected by Fermi have still no firmly established counterpart at lower energies. Here we propose a new approach to find candidate counterparts for the unidentified gamma-ray sources (UGSs) based on the 325 MHz radio survey performed with Westerbork Synthesis Radio Telescope (WSRT) in the northern hemisphere. First we investigate the low-frequency radio properties of blazars, the largest known population of gamma-ray sources; then we search for sources with similar radio properties combining the information derived from the Westerbork Northern Sky Survey (WENSS) with those of the NRAO VLA Sky survey (NVSS). We present a list of candidate counterparts for 32 UGSs with at least one counterpart in the WENSS. We also performed an extensive research in literature to look for infrared and optical counterparts of the gamma-ray blazar candidates selected with the low-frequency radio observations to confirm their nature. On the basis of our multifrequency research we identify 23 new gamma-ray blazar candidates out of 32 UGSs investigated. I will also present the first analysis of very low frequency radio emission of blazars based on the recent Very Large Array Low-Frequency Sky Survey (VLSS) at 74 MHz. I show that blazars present radio flat spectra when evaluated at 74 MHz, about an order of magnitude in frequency lower than previous analyses. The implications of these findings in the contest of the blazars – radio galaxies connection will be discussed.

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.

Very Large Array imaging of five Fanaroff-Riley II 3CR radio galaxies

1993 ◽  
Vol 105 ◽  
pp. 1690 ◽  
Author(s):  
Ilias Fernini ◽  
Jack O. Burns ◽  
Alan H. Bridle ◽  
Rick A. Perley
Keyword(s):  
Radio Galaxies ◽  
Large Array ◽  
Very Large Array ◽  
Array Imaging

scholarly journals Radio emission in ultracool dwarfs: The nearby substellar triple system VHS 1256–1257

2018 ◽  
Vol 610 ◽  
pp. A23 ◽  
Author(s):  
J. C. Guirado ◽  
R. Azulay ◽  
B. Gauza ◽  
M. A. Pérez-Torres ◽  
R. Rebolo ◽  
...  
Keyword(s):  
Radio Emission ◽  
Flux Density ◽  
Upper Bound ◽  
Equal Mass ◽  
Large Array ◽  
Turnover Frequency ◽  
Radio Flux ◽  
Very Large Array ◽  
Upper Limit ◽  
Low Mass

Aim. With the purpose of investigating the radio emission of new ultracool objects, we carried out a targeted search in the recently discovered system VHS J125601.92–125723.9 (hereafter VHS 1256–1257); this system is composed by an equal-mass M7.5 binary and a L7 low-mass substellar object located at only 15.8 pc. Methods. We observed in phase-reference mode the system VHS 1256–1257 with the Karl G. Jansky Very Large Array at X band and L band and with the European VLBI Network at L band in several epochs during 2015 and 2016. Results. We discovered radio emission at X band spatially coincident with the equal-mass M7.5 binary with a flux density of 60 μJy. We determined a spectral index α = −1.1 ± 0.3 between 8 and 12 GHz, suggesting that non-thermal, optically thin, synchrotron, or gyrosynchrotron radiation is responsible for the observed radio emission. Interestingly, no signal is seen at L band where we set a 3σ upper limit of 20 μJy. This might be explained by strong variability of the binary or self-absorption at this frequency. By adopting the latter scenario and gyrosynchrotron radiation, we constrain the turnover frequency to be in the interval 5–8.5 GHz, from which we infer the presence of kG-intense magnetic fields in the M7.5 binary. Our data impose a 3σ upper bound to the radio flux density of the L7 object of 9 μJy at 10 GHz.

scholarly journals Radio Images of Planetary Nebulae

1989 ◽  
Vol 131 ◽  
pp. 17-28 ◽  
Author(s):  
Yervant Terzian
Keyword(s):  
Magnetic Field ◽  
Neutral Hydrogen ◽  
Planetary Nebulae ◽  
Aperture Synthesis ◽  
Large Array ◽  
Very Large Array ◽  
Upper Limit ◽  
Neutral Material ◽  
Continuum Radio ◽  
The Continuum

The continuum radio spectra of planetary nebulae are discussed, and the structure of these objects is examined from the observed aperture synthesis brightness distributions determined with the Very Large Array. The use of radio observations in determining distances to planetary nebulae is examined. The detection of atomic neutral hydrogen at λ21 cm associated with planetary nebulae, as well as the associated CO and OH components are discussed. An upper limit, of the nebular magnetic field associated with the neutral material, of 1mG is reported for NGC 6302.

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