scholarly journals The nature of the faint low-frequency radio source population

2017 ◽  
Vol 468 (1) ◽  
pp. 1156-1168 ◽  
Author(s):  
E. F. Ocran ◽  
A. R. Taylor ◽  
M. Vaccari ◽  
D. A. Green
Keyword(s):  
Radio Source ◽  
Low Frequency ◽  
Source Population

scholarly journals Unveiling the high-frequency radio source population with the AT20G survey

2013 ◽  
Vol 9 (S304) ◽  
pp. 205-208
Author(s):  
Elizabeth K. Mahony
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
High Frequency ◽  
Gamma Ray ◽  
Low Frequency ◽  
Radio Sources ◽  
Source Population ◽  
Frequency Source ◽  
Galaxy Population ◽  
5 Ghz

AbstractUntil recently, the radio sky above 5 GHz was relatively unexplored. This has changed with the completion of the Australia Telescope 20 GHz survey (AT20G; Murphy et al., 2010); a blind survey of the southern sky down to a limiting flux density of 40 mJy. The AT20G survey provides by far the largest and most complete sample of high-frequency radio sources yet obtained, offering new insights into the nature of the high-frequency active galaxy population. Whilst the radio data provides a unique sample of objects, these data alone are insufficient to completely constrain models of radio source properties and the evolution of radio galaxies. Complementary multiwavelength data is vital in understanding the physical properties of the central black hole.In this talk I will provide a brief overview of the AT20G survey, followed by a discussion of the multiwavelength properties of the high-frequency source population. In particular, I will focus on the optical properties of AT20G sources, which are very different to those of a low-frequency selected sample, along with the gamma-ray properties where we find a correlation between high-frequency radio flux density and gamma-ray flux density. By studying the multiwavelength properties of a large sample of high-frequency radio sources we gain a unique perspective on the inner dynamics of some of the most active AGN.

scholarly journals Interpretation of Source Counts and Redshift Data in Evolutionary Universes

1977 ◽  
Vol 74 ◽  
pp. 269-277
Author(s):  
J. V. Wall ◽  
T. J. Pearson ◽  
M. S. Longair
Keyword(s):  
Radio Source ◽  
High Frequency ◽  
Low Frequency ◽  
Physical Basis ◽  
Source Population ◽  
Cosmic Evolution ◽  
Survey Population ◽  
Frequency Survey ◽  
Source Populations ◽  
Luminosity Evolution

Conventional interpretation of the N(S) relation requires cosmic evolution of the radio source population. Investigators agree on the general features of this evolution: it must be confined to the most luminous sources, and must be strong, the numbers of such sources at redshifts of 1 to 4 exceeding the present numbers by a factor ≳103. There is no consensus as to whether density or luminosity evolution prevails (or both), whether a cutoff in redshift is necessary, or whether the source populations found in high-frequency surveys follow even the general evolutionary picture deduced for the low-frequency survey population. It is therefore hardly surprising that the physical basis of the evolution, the ultimate goal of N(S) interpretation, remains largely “in the realm of imaginative speculation” (P. A. G. Scheuer).

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.

scholarly journals Systematic effects in LOFAR data: A unified calibration strategy

2019 ◽  
Vol 622 ◽  
pp. A5 ◽  
Author(s):  
F. de Gasperin ◽  
T. J. Dijkema ◽  
A. Drabent ◽  
M. Mevius ◽  
D. Rafferty ◽  
...  
Keyword(s):  
Spectral Energy Distribution ◽  
Low Frequency ◽  
Reduction Process ◽  
Spectral Energy ◽  
Ionospheric Scintillation ◽  
Source Population ◽  
Full Data ◽  
Low Frequencies ◽  
Beam Shape ◽  
Systematic Effects

Context. New generation low-frequency telescopes are exploring a new parameter space in terms of depth and resolution. The data taken with these interferometers, for example with the LOw Frequency ARray (LOFAR), are often calibrated in a low signal-to-noise ratio regime and the removal of critical systematic effects is challenging. The process requires an understanding of their origin and properties. Aim. In this paper we describe the major systematic effects inherent to next generation low-frequency telescopes, such as LOFAR. With this knowledge, we introduce a data processing pipeline that is able to isolate and correct these systematic effects. The pipeline will be used to calibrate calibrator observations as the first step of a full data reduction process. Methods. We processed two LOFAR observations of the calibrator 3C 196: the first using the Low Band Antenna (LBA) system at 42–66 MHz and the second using the High Band Antenna (HBA) system at 115–189 MHz. Results. We were able to isolate and correct for the effects of clock drift, polarisation misalignment, ionospheric delay, Faraday rotation, ionospheric scintillation, beam shape, and bandpass. The designed calibration strategy produced the deepest image to date at 54 MHz. The image has been used to confirm that the spectral energy distribution of the average radio source population tends to flatten at low frequencies. Conclusions. We prove that LOFAR systematic effects can be described by a relatively small number of parameters. Furthermore, the identification of these parameters is fundamental to reducing the degrees of freedom when the calibration is carried out on fields that are not dominated by a strong calibrator.

scholarly journals Star Formation Rates in Lyman Break Galaxies: Radio Stacking of LBGs in the COSMOS Field and the Sub‐μJy Radio Source Population

2008 ◽  
Vol 689 (2) ◽  
pp. 883-888 ◽  
Author(s):  
C. L. Carilli ◽  
Nicholas Lee ◽  
P. Capak ◽  
E. Schinnerer ◽  
K.‐S. Lee ◽  
...  
Keyword(s):  
Star Formation ◽  
Radio Source ◽  
Source Population ◽  
Lyman Break Galaxies

scholarly journals Radio Source Surveys

2002 ◽  
Vol 199 ◽  
pp. 3-10
Author(s):  
J. J. Condon
Keyword(s):  
Radio Source ◽  
Source Parameters ◽  
Low Frequency ◽  
Low Frequencies ◽  
Cluster Emission ◽  
New Class ◽  
Basic Source ◽  
Nearby Galaxies ◽  
Source Populations ◽  
Compact Sources

The primary goal of radio source surveys is to generate flux-limited samples. Sources selected at very low frequencies are dominated by unbeamed emission and give the only unbiased view of the parent populations used by “unification” models to account for the diversity of sources seen at high frequencies. Low-frequency surveys favor sources with exceptionally steep spectra. They include radio galaxies at high redshifts, radio halos of nearby galaxies, relic radio sources, diffuse cluster emission, pulsars that may be missed by traditional pulse searches, and a new class of unidentified compact sources. Flux densities from low-frequency surveys extend the spectra of known source populations to frequencies at which free-free and synchrotron absorption become significant and constrain basic source parameters. Finally, telescope fields-of-view scale ∝ λ2, so gridded surveys can be more efficient than directed observations of individual targets. This review covers recent and proposed low-frequency source surveys and their astronomical uses.

scholarly journals A Comparison of the Structures of 3CR Quasars and Blank Field Radio Sources

1982 ◽  
Vol 97 ◽  
pp. 435-436 ◽  
Author(s):  
F. N. Owen ◽  
J. J. Puschell ◽  
R. A. Laing
Keyword(s):  
Radio Source ◽  
Structural Properties ◽  
Low Frequency ◽  
Radio Sources ◽  
Blank Field ◽  
Sky Survey

The purpose of this communication is to update our knowledge of the radio structural properties of quasars and blank field radio sources (blank field ≡ any radio source without an identification on the Palomar Sky Survey prints). The quasar sample consists of all sources (25) with angular sizes greater than 10 arcsec in the list of Jodrell Bank quasars observed by Owen, Porcas and Neff (1978). The blank fields consist of 16 3CR sources also with structures >10 arcsec based on Cambridge 5 km telescope observations. The sources were selected in low-frequency surveys; their emission at ν < 1 GHz is dominated by extended components with steep spectra. Thus, both samples should be oriented randomly in space except for a slight bias to be in the plane of the sky.

scholarly journals The duty cycle of radio galaxies revealed by LOFAR: remnant and restarted radio source populations in the Lockman Hole

2020 ◽  
Vol 496 (2) ◽  
pp. 1706-1717 ◽  
Author(s):  
Stanislav S Shabala ◽  
Nika Jurlin ◽  
Raffaella Morganti ◽  
Marisa Brienza ◽  
Martin J Hardcastle ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Radio Source ◽  
Low Frequency ◽  
Galactic Nuclei ◽  
Radio Jets ◽  
Modelling Analysis ◽  
Self Consistent ◽  
Large Populations ◽  
Source Populations ◽  
Lockman Hole

ABSTRACT Feedback from radio jets associated with active galactic nuclei (AGNs) plays a profound role in the evolution of galaxies. Kinetic power of these radio jets appears to show temporal variation, but the mechanism(s) responsible for this process are not yet clear. Recently, the LOw Frequency ARray (LOFAR) has uncovered large populations of active, remnant, and restarted radio jet populations. By focusing on LOFAR data in the Lockman Hole, in this work we use the Radio AGNs in Semi-Analytic Environments (RAiSE) dynamical model to present the first self-consistent modelling analysis of active, remnant, and restarted radio source populations. Consistent with other recent work, our models predict that remnant radio lobes fade quickly. Any high (&gt;10 per cent) observed fraction of remnant and restarted sources therefore requires a dominant population of short-lived jets. We speculate that this could plausibly be provided by feedback-regulated accretion.

scholarly journals Spectroscopy of faint radio sources: the nature of the sub-mJy radio-source population

1993 ◽  
Vol 263 (1) ◽  
pp. 98-122 ◽  
Author(s):  
C. R. Benn ◽  
M. Rowan-Robinson ◽  
R. G. McMahon ◽  
T. J. Broadhurst ◽  
A. Lawrence
Keyword(s):  
Radio Source ◽  
Radio Sources ◽  
Source Population

scholarly journals The radio source population at high frequency: follow-up of the 15-GHz 9C survey

2004 ◽  
Vol 354 (2) ◽  
pp. 485-521 ◽  
Author(s):  
R. C. Bolton ◽  
G. Cotter ◽  
G. G. Pooley ◽  
J. M. Riley ◽  
E. M. Waldram ◽  
...  
Keyword(s):  
Radio Source ◽  
High Frequency ◽  
Source Population
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