scholarly journals The ATLAS 9.0 GHz survey of the extended Chandra Deep Field South: the faint 9.0 GHz radio population

2019 ◽  
Vol 491 (3) ◽  
pp. 3395-3410 ◽  
Author(s):  
M T Huynh ◽  
N Seymour ◽  
R P Norris ◽  
T Galvin
Keyword(s):  
Radio Emission ◽  
Active Galactic Nuclei ◽  
Radio Source ◽  
Galactic Nuclei ◽  
Radio Galaxies ◽  
Significant Fraction ◽  
Radio Sources ◽  
Star Forming ◽  
Source Populations ◽  
Compact Array

ABSTRACT We present a new image of the 9.0 GHz radio emission from the extended Chandra Deep Field South. A total of 181 h of integration with the Australia Telescope Compact Array has resulted in a 0.276 deg2 image with a median sensitivity of ∼20 µJy beam−1 rms, for a synthesized beam of 4.0 × 1.3 arcsec. We present a catalogue of the 9.0 GHz radio sources, identifying 70 source components and 55 individual radio galaxies. Source counts derived from this sample are consistent with those reported in the literature. The observed source counts are also generally consistent with the source counts from simulations of the faint radio population. Using the wealth of multiwavelength data available for this region, we classify the faint 9 GHz population and find that 91 per cent are radio-loud active galactic nuclei (AGNs), 7 per cent are radio-quiet AGNs, and 2 per cent are star-forming galaxies. The 9.0 GHz radio sources were matched to 5.5 and 1.4 GHz sources in the literature and we find a significant fraction of flat or inverted spectrum sources, with 36 per cent of the 9 GHz sources having $\alpha _{5.5\,\mathrm{ GHz}}^{9.0\,\mathrm{ GHz}}$ > −0.3 (for S ∝ να). This flat or inverted population is not well reproduced by current simulations of radio source populations.

The GLEAM 4-Jy Sample: The brightest radio-sources in the southern sky

2019 ◽  
Vol 15 (S356) ◽  
pp. 375-375
Author(s):  
Sarah White
Keyword(s):  
Radio Emission ◽  
Active Galactic Nuclei ◽  
Visual Inspection ◽  
Low Frequency ◽  
Galactic Nuclei ◽  
Radio Sources ◽  
Relativistic Jets ◽  
The Galaxy ◽  
Murchison Widefield Array ◽  
Past Activity

AbstractLow-frequency radio emission allows powerful active galactic nuclei (AGN) to be selected in a way that is unaffected by dust obscuration and orientation of the jet axis. It also reveals past activity (e.g. radio lobes) that may not be evident at higher frequencies. Currently, there are too few “radio-loud” galaxies for robust studies in terms of redshift-evolution and/or environment. Hence our use of new observations from the Murchison Widefield Array (the SKA-Low precursor), over the southern sky, to construct the GLEAM 4-Jy Sample (1,860 sources at S151MHz > 4 Jy). This sample is dominated by AGN and is 10 times larger than the heavily relied-upon 3CRR sample (173 sources at S178MHz > 10 Jy) of the northern hemisphere. In order to understand how AGN influence their surroundings and the way galaxies evolve, we first need to correctly identify the galaxy hosting the radio emission. This has now been completed for the GLEAM 4-Jy Sample – through repeated visual inspection and extensive checks against the literature – forming a valuable, legacy dataset for investigating relativistic jets and their interplay with the environment.

scholarly journals VSOP, A Space VLBI Programme

1990 ◽  
Vol 123 ◽  
pp. 263-269
Author(s):  
H. Hirabayashi
Keyword(s):  
Active Galactic Nuclei ◽  
Phase Transfer ◽  
Galactic Nuclei ◽  
Satellite Orbit ◽  
Radio Sources ◽  
Space Observatory ◽  
Stellar Objects ◽  
Radio Observatory ◽  
Star Forming ◽  
Star Forming Regions

AbstractVSOP, VLBI Space Observatory Programme, is an approved space VLBI programme of ISAS for the study of very compact radio sources with the synthesized aperture of 30,000 km diameter, by connecting an orbiting radio observatory with ground radiotelescopes. The VSOP satellite carrying 10 m antenna with 1.6, 5, and 22 GHz band receivers will be launched in early 1995 by M-V rocket of ISAS into an eccentric orbit with 20,000 km in apogee height. The tracking network will be formed for the satellite orbit determination, phase transfer and IF down-link. VSOP aims imaging capability with best resolution of 0.0001 arc second in 22 GHz band. Imaging of active galactic nuclei, star forming regions and stellar objects, and radioastrometry are main scientific targets.

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 (>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 The AGN content of deep radio surveys and radio emission in radio-quiet AGN. Why every astronomer should care about deep radio fields

2013 ◽  
Vol 9 (S304) ◽  
pp. 79-85
Author(s):  
P. Padovani ◽  
M. Bonzini ◽  
N. Miller ◽  
K. I. Kellermann ◽  
V. Mainieri ◽  
...  
Keyword(s):  
Star Formation ◽  
Radio Emission ◽  
Radio Galaxies ◽  
X Ray ◽  
Star Forming ◽  
Luminosity Functions ◽  
Radio Number ◽  
Source Populations ◽  
Number Counts ◽  
Quasars And Radio Galaxies

AbstractWe present our very recent results on the sub-mJy radio source populations at 1.4 GHz based on the Extended Chandra Deep Field South VLA survey, which reaches ~ 30 μJy, with details on their number counts, evolution, and luminosity functions. The sub-mJy radio sky turns out to be a complex mix of star-forming galaxies and radio-quiet AGN evolving at a similar, strong rate and declining radio-loud AGN. While the well-known flattening of the radio number counts below 1 mJy is mostly due to star-forming galaxies, these sources and AGN make up an approximately equal fraction of the sub-mJy sky. Our results shed also light on a fifty-year-old issue, namely radio emission from radio-quiet AGN, and suggest that it is closely related to star formation, at least at z ~ 1.5 − 2. The implications of our findings for future, deeper radio surveys, including those with the Square Kilometre Array, are also discussed. One of the main messages, especially to non-radio astronomers, is that radio surveys are reaching such faint limits that, while previously they were mainly useful for radio quasars and radio galaxies, they are now detecting mostly star-forming galaxies and radio-quiet AGN, i.e., the bulk of the extragalactic sources studied in the infrared, optical, and X-ray bands.

scholarly journals The ATESP 5 GHz radio survey

2018 ◽  
Vol 621 ◽  
pp. A19
Author(s):  
R. Ricci ◽  
I. Prandoni ◽  
H. R. De Ruiter ◽  
P. Parma
Keyword(s):  
High Resolution ◽  
Radio Emission ◽  
Radio Galaxies ◽  
Host Galaxy ◽  
Radio Sources ◽  
Early Type ◽  
Host Galaxies ◽  
Star Forming ◽  
Open Questions ◽  
5 Ghz

Aims. It is now established that the faint radio population is a mixture of star-forming galaxies and faint active galactic nuclei (AGNs), with the former dominating below S1.4 GHz ∼ 100μJy and the latter at larger flux densities. The faint radio AGN component can itself be separated into two main classes, mainly based on the host-galaxy properties: sources associated with red/early-type galaxies (like radio galaxies) are the dominant class down to ∼100 μJy; quasar/Seyfert–like sources contribute an additional 10–20%. One of the major open questions regarding faint radio AGNs is the physical process responsible for their radio emission. This work aims at investigating this issue, with particular respect to the AGN component associated with red/early-type galaxies. Such AGNs show, on average, flatter radio spectra than radio galaxies and are mostly compact (≤30 kpc in size). Various scenarios have been proposed to explain their radio emission. For instance they could be core/core-jet dominated radio galaxies, low-power BL Lacertae, or advection-dominated accretion flow (ADAF) systems. Methods. We used the Australia Telescope Compact Array (ATCA) to extend a previous follow-up multi-frequency campaign to 38 and 94 GHz. This campaign focuses on a sample of 28 faint radio sources associated with early-type galaxies extracted from the ATESP 5 GHz survey. Such data, together with those already at hand, are used to perform radio spectral and variability analyses. Both analyses can help us to disentangle between core- and jet-dominated sources, as well as to verify the presence of ADAF/ADAF+jet systems. Additional high-resolution observations at 38 GHz were carried out to characterise the radio morphology of these sources on kiloparsec scales. Results. Most of the sources (25/28) were detected at 38 GHz, while only one (ATESP5J224547−400324) of the twelve sources observed at 94 GHz was detected. From the analysis of the radio spectra we confirmed our previous findings that pure ADAF models can be ruled out. Only eight out of the 28 sources were detected in the 38-GHz high-resolution (0.6 arcsec) radio images and of those eight only one showed a tentative core-jet structure. Putting together spectral, variability, luminosity, and linear size information we conclude that different kinds of sources compose our AGN sample: (a) luminous and large (≥100 kpc) classical radio galaxies (∼18% of the sample); (b) compact (confined within their host galaxies), low-luminosity, power-law (jet-dominated) sources (∼46% of the sample); and (c) compact, flat (or peaked) spectrum, presumably core-dominated, radio sources (∼36% of the sample). Variability is indeed preferentially associated with the latter.

scholarly journals Optical Spectra of Radio-Loud and Radio-Quiet Active Galactic Nuclei

1982 ◽  
Vol 97 ◽  
pp. 369-371 ◽  
Author(s):  
Donald E. Osterbrock
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Radio Galaxies ◽  
Optical Spectra ◽  
Emission Lines ◽  
Radio Sources ◽  
Strong Emission ◽  
Normal Galaxies ◽  
Many Sources

Many radio galaxies have strong emission lines in their optical spectra. The fraction with such lines is much larger than in “normal” galaxies. Radio galaxies generally also have very bright nuclei; thus those with strong emission lines are similar in both respects to Seyfert galaxies. Hence radio and Seyfert galaxies are both generally considered to be similar physical objects: active galactic nuclei. Their observational properties show they are closely related to quasars (quasi-stellar radio sources) and (radio-quiet) QSOs. A short table of the space density of these objects, culled from many sources, chiefly Schmidt (1978) and Simkim, Su and Schwarz (1980) is given below. Although all the numbers are quite uncertain, there is no doubt that the radio-loud objects are relatively rare. With less certainty, it appears that the ratio of numbers of radio galaxies to Seyfert galaxies is about the same as the ratio of numbers of quasars to QSOs.

scholarly journals Discovery of Rare Dying Radio Galaxies Using MeerKAT

Galaxies ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 102
Author(s):  
Nadeem Oozeer ◽  
Lawrence Rudnick ◽  
Michael F. Bietenholz ◽  
Tiziana Venturi ◽  
Kenda Knowles ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Radio Galaxy ◽  
Galaxy Cluster ◽  
Galactic Nuclei ◽  
Radio Galaxies ◽  
Radio Sources ◽  
Central Black Hole ◽  
Massive Galaxies ◽  
Multi Wavelength ◽  
Radio Power

Dying radio galaxies represent a stage of the evolution of active galactic nuclei (AGN), during which the accreting central black hole has switched off and/or falls to such a low level that the plasma outflow can no longer be sustained. When this happens, the radio source undergoes a period of fading, the dying phase, before it disappears completely. We present the study of three potential dying radio sources using the MeerKAT radio telescope: MKT J072851.2-752743, MKT J001940.4-654722, and ACO 548B. The identification as dying radio sources came from the MeerKAT Galaxy Cluster Legacy Survey (MGCLS). We carry out a multi-wavelength analysis of the sources and derive their energetics. The ages of the sources are ∼30–70 Myr, they have magnetic fields of the order of a few μG, and they have relatively low radio power. Their potential optical counterparts are associated with massive galaxies. We show that ACO 548B, previously classified as two peripheral relic radio sources, is a dying radio galaxy. With its good sensitivity and resolution, MeerKAT is an ideal instrument to detect potential dying radio sources, and contribute to the understanding of the evolution of AGN population.

scholarly journals Radio Active Nuclei

1983 ◽  
Vol 6 ◽  
pp. 481-490
Author(s):  
K. I. Kellermann
Keyword(s):  
Active Galactic Nuclei ◽  
Time Scale ◽  
Galactic Nuclei ◽  
Extreme Case ◽  
Radio Galaxies ◽  
Radio Sources ◽  
Great Similarity ◽  
Radio Flux ◽  
Active Nucleus ◽  
Origin And Evolution

For the purpose of this survey we shall use the term radio active nucleus to refer to compact radio sources which are found in galactic nuclei and which show activity either in the form of flux density variations or outward flow of material from the nucleus. There is great similarity between the observed properties of radio active nuclei with those of radio active quasars, and it is widely supposed that the quasar phenomena represents an extreme case of an active galaxy. In this paper however, we shall concentrate on compact radio sources found in the nuclei of identifiable galaxies, and quasars are discussed only to the extent that they help to understand the origin and evolution of radio active galactic nuclei.Since radio active nuclei are typically in extent, they can be mapped only with VLBI techniques. Detailed maps are available for only a few of the strongest nuclei, but a much larger number can be identified from conventional interferometry with a resolution ~ 1”. In the few radio galaxies where most of the observed radio flux comes from the active nucleus, activity is observed directly on a time scale of months or even weeks. In others, it may be inferred from arguments based on synchrotron lifetime.

scholarly journals Deep LOFAR 150 MHz imaging of the Boötes field: Unveiling the faint low-frequency sky

2018 ◽  
Vol 620 ◽  
pp. A74 ◽  
Author(s):  
E. Retana-Montenegro ◽  
H. J. A. Röttgering ◽  
T. W. Shimwell ◽  
R. J. van Weeren ◽  
I. Prandoni ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Angular Resolution ◽  
Low Frequency ◽  
Galactic Nuclei ◽  
Radio Sources ◽  
Low Frequencies ◽  
Star Forming ◽  
Radio Imaging ◽  
Deep Survey ◽  
Systematic Effects

We have conducted a deep survey (with a central rms of 55 μJy) with the LOw Frequency ARray (LOFAR) at 120–168 MHz of the Boötes field, with an angular resolution of 3.98″ × 6.45″, and obtained a sample of 10 091 radio sources (5σ limit) over an area of 20 deg2. The astrometry and flux scale accuracy of our source catalog is investigated. The resolution bias, incompleteness and other systematic effects that could affect our source counts are discussed and accounted for. The derived 150 MHz source counts present a flattening below sub-mJy flux densities, that is in agreement with previous results from high- and low- frequency surveys. This flattening has been argued to be due to an increasing contribution of star-forming galaxies and faint active galactic nuclei. Additionally, we use our observations to evaluate the contribution of cosmic variance to the scatter in source counts measurements. The latter is achieved by dividing our Boötes mosaic into 10 non-overlapping circular sectors, each one with an approximate area of 2 deg2. The counts in each sector are computed in the same way as done for the entire mosaic. By comparing the induced scatter with that of counts obtained from depth observations scaled to 150 MHz, we find that the 1σ scatter due to cosmic variance is larger than the Poissonian errors of the source counts, and it may explain the dispersion from previously reported depth source counts at flux densities S <  1 mJy. This work demonstrates the feasibility of achieving deep radio imaging at low-frequencies with LOFAR.

scholarly journals The XXL Survey

2018 ◽  
Vol 620 ◽  
pp. A3 ◽  
Author(s):  
Andrew Butler ◽  
Minh Huynh ◽  
Jacinta Delhaize ◽  
Vernesa Smolčić ◽  
Anna Kapińska ◽  
...  
Keyword(s):  
Radio Source ◽  
Galactic Nuclei ◽  
Spectral Energy ◽  
Radio Sources ◽  
Density Level ◽  
Energy Distributions ◽  
Sky Survey ◽  
Multiple Component ◽  
Good Agreement ◽  
Compact Array

The 2.1 GHz radio source catalogue of the 25 deg2 ultimate XMM extragalactic survey south (XXL-S) field, observed with the Australia Telescope Compact Array (ATCA), is presented. The final radio mosaic achieved a resolution of ~ 4.8″ and a median rms noise of σ ≈ 41 μJy/beam. To date, this is the largest area radio survey to reach this flux density level. A total of 6350 radio components above 5σ are included in the component catalogue, 26.4% of which are resolved. Of these components, 111 were merged together to create 48 multiple-component radio sources, resulting in a total of 6287 radio sources in the source catalogue, 25.9% of which were resolved. A survival analysis revealed that the median spectral index of the Sydney University Molonglo Sky Survey (SUMSS) 843 MHz sources in the field is α = −0.75, consistent with the values of − 0.7 to − 0.8 commonly used to characterise radio spectral energy distributions of active galactic nuclei. The 2.1 GHz and 1.4 GHz differential radio source counts are presented and compared to other 1.4 GHz radio surveys. The XXL-S source counts show good agreement with the other surveys.

Sign in / Sign up

Export Citation Format

Share Document