scholarly journals Probing the Wind Component of Radio Emission in Luminous High-redshift Quasars

2021 ◽  
Vol 162 (6) ◽  
pp. 270
Author(s):  
Gordon T. Richards ◽  
Trevor V. McCaffrey ◽  
Amy Kimball ◽  
Amy L. Rankine ◽  
James H. Matthews ◽  
...  
Keyword(s):  
Star Formation ◽  
Radio Emission ◽  
Survey Data ◽  
Accretion Disk ◽  
High Redshift ◽  
Nonlinear Function ◽  
Wind Component ◽  
Radio Observations ◽  
Very Large Array ◽  
Radio Detection

Abstract We discuss a probe of the contribution of wind-related shocks to the radio emission in otherwise radio-quiet quasars. Given (1) the nonlinear correlation between UV and X-ray luminosity in quasars, (2) that such a correlation leads to higher likelihood of radiation-line-driven winds in more luminous quasars, and (3) that luminous quasars are more abundant at high redshift, deep radio observations of high-redshift quasars are needed to probe potential contributions from accretion disk winds. We target a sample of 50 z ≃ 1.65 color-selected quasars that span the range of expected accretion disk wind properties as traced by broad C iv emission. 3 GHz observations with the Very Large Array to an rms of ≈10 μJy beam−1 probe to star formation rates of ∼400 M ⊙ yr−1, leading to 22 detections. Supplementing these pointed observations are survey data of 388 sources from the LOFAR Two-meter Sky Survey Data Release 1 that reach comparable depth (for a typical radio spectral index), where 123 sources are detected. These combined observations reveal a radio detection fraction that is a nonlinear function of C iv emission-line properties and suggest that the data may require multiple origins of radio emission in radio-quiet quasars. We find evidence for radio emission from weak jets or coronae in radio-quiet quasars with low Eddington ratios, with either (or both) star formation and accretion disk winds playing an important role in optically luminous quasars and correlated with increasing Eddington ratio. Additional pointed radio observations are needed to fully establish the nature of radio emission in radio-quiet quasars.

scholarly journals Fundamental differences in the radio properties of red and blue quasars: enhanced compact AGN emission in red quasars

2020 ◽  
Vol 494 (4) ◽  
pp. 4802-4818 ◽  
Author(s):  
V A Fawcett ◽  
D M Alexander ◽  
D J Rosario ◽  
L Klindt ◽  
S Fotopoulou ◽  
...  
Keyword(s):  
Star Formation ◽  
Radio Emission ◽  
Sloan Digital Sky Survey ◽  
Formation Processes ◽  
Very Large Array ◽  
Radio Detection ◽  
Extended Radio ◽  
Sky Survey ◽  
Tentative Evidence ◽  
Insight Into

ABSTRACT We have recently used the Faint Images of the Radio Sky at Twenty-centimeters (FIRST) survey to show that red quasars have fundamentally different radio properties to typical blue quasars: a significant (factor ≈3) enhancement in the radio-detection fraction, which arises from systems around the radio-quiet threshold with compact (<5 arcsec) radio morphologies. To gain greater insight into these physical differences, here we use the DR14 Sloan Digital Sky Survey (SDSS) and more sensitive, higher resolution radio data from the Very Large Array (VLA) Stripe 82 (S82) and VLA-COSMOS 3 GHz (C3GHz) surveys. With the S82 data, we perform morphological analyses at a resolution and depth three times that of the FIRST radio survey, and confirm an enhancement in radio-faint and compact red quasars over typical quasars; we now also find tentative evidence for an enhancement in red quasars with slightly extended radio structures (16–43 kpc at z = 1.5). These analyses are complemented by C3GHz, which is deep enough to detect radio emission from star-formation processes. From our data we find that the radio enhancement from red quasars is due to AGN activity on compact scales (≲43 kpc) for radio-intermediate–radio-quiet sources (−5 < $\mathcal {R}$ < −3.4, where $\mathcal {R}$ = $L_{\rm{1.4\,GHz}}/L_{6\mu\text{m}}$), which decreases at $\mathcal {R}$ < −5 as the radio emission from star-formation starts to dilute the AGN component. Overall our results argue against a simple orientation scenario and are consistent with red quasars representing a younger, earlier phase in the overall evolution of quasars.

scholarly journals A radio polarimetric study to disentangle AGN activity and star formation in Seyfert galaxies

2020 ◽  
Vol 499 (1) ◽  
pp. 334-354
Author(s):  
Biny Sebastian ◽  
P Kharb ◽  
C P O’Dea ◽  
J F Gallimore ◽  
S A Baum
Keyword(s):  
Star Formation ◽  
Radio Emission ◽  
Seyfert Galaxies ◽  
Starburst Galaxies ◽  
Shock Acceleration ◽  
Very Large Array ◽  
Star Forming ◽  
Array Configuration ◽  
Star Forming Regions ◽  
Tentative Evidence

ABSTRACT To understand the origin of radio emission in radio-quiet active galactic nucleus (AGN) and differentiate between the contributions from star formation, AGN accretion, and jets, we have observed a nearby sample of Seyfert galaxies along with a comparison sample of starburst galaxies using the Expanded Very Large Array (EVLA) in full-polarization mode in the B-array configuration. The radio morphologies of the Seyfert galaxies show lobe/bubble-like features or prominent cores in radio emission, whereas the starburst galaxies show radio emission spatially coincident with the star-forming regions seen in optical images. There is tentative evidence that Seyferts tend to show more polarized structures than starburst galaxies at the resolution of our observations. We find that unlike a sample of Seyfert galaxies hosting kilo-parsec scale radio (KSR) emission, starburst galaxies with superwinds do not show radio-excess compared to the radio–FIR correlation. This suggests that shock acceleration is not adequate to explain the excess radio emission seen in Seyferts and hence most likely have a jet-related origin. We also find that the [O iii] luminosity of the Seyferts is correlated with the off-nuclear radio emission from the lobes, whereas it is not well correlated with the total emission which also includes the core. This suggests strong jet–medium interaction, which in turn limits the jet/lobe extents in Seyferts. We find that the power contribution of AGN jet, AGN accretion, and star formation is more or less comparable in our sample of Seyfert galaxies. We also find indications of episodic AGN activity in many of our Seyfert galaxies.

scholarly journals Radio morphology of southern narrow-line Seyfert 1 galaxies with Very Large Array observations*

2020 ◽  
Vol 498 (1) ◽  
pp. 1278-1297
Author(s):  
S Chen ◽  
E Järvelä ◽  
L Crepaldi ◽  
M Zhou ◽  
S Ciroi ◽  
...  
Keyword(s):  
Star Formation ◽  
Radio Emission ◽  
Large Mass ◽  
Large Array ◽  
Narrow Line ◽  
Diffuse Emission ◽  
Jets And Outflows ◽  
Very Large Array ◽  
Radio Jets ◽  
New Radio

ABSTRACT We present the results of new radio observations carried out with the Karl G. Jansky Very Large Array C-configuration at 5.5 GHz for a sample of southern narrow-line Seyfert 1 galaxies (NLS1s). This work increases the number of known radio-detected NLS1s in the Southern hemisphere, and confirms that the radio emission of NLS1s is mainly concentrated in a central region at kpc-scale and only a few sources show diffuse emission. In radio-quiet NLS1s, the radio luminosity tends to be higher in steep-spectrum sources and be lower in flat-spectrum sources, which is opposite to radio-loud NLS1s. This may be because the radio emission of steep NLS1s is dominated by misaligned jets, active galactic nucleus driven outflows, or star formation superposing on a compact core. Instead the radio emission of flat NLS1s may be produced by a central core that has not yet developed radio jets and outflows. We discover new NLS1s harbouring kpc-scale radio jets and confirm that a powerful jet does not require a large-mass black hole to be generated. We also find sources dominated by star formation. These NLS1s could be new candidates in investigating the radio emission of different mechanisms.

scholarly journals Radio Emission from WR Stars

1982 ◽  
Vol 99 ◽  
pp. 221-224 ◽  
Author(s):  
David E. Hogg
Keyword(s):  
Simple Model ◽  
Radio Emission ◽  
Mass Loss ◽  
Flux Density ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Large Array ◽  
Radio Observations ◽  
Very Large Array

In principle radio observations of WR stars offer the best possibility of determining the rate of mass loss, since for a simple model of the extended atmosphere the mass loss rate depends primarily on quantities—the flux density, the velocity, and the distance—which are observable (Barlow 1979). Until now, detections of Wolf-Rayet stars have been limited by the sensitivity and resolution of available telescopes. The advent of the Very Large Array makes a search for emission from a large number of these stars feasible.

scholarly journals GASP XXXVIII: The LOFAR-MeerKAT-VLA View on the Nonthermal Side of a Jellyfish Galaxy

2022 ◽  
Vol 924 (2) ◽  
pp. 64
Author(s):  
Alessandro Ignesti ◽  
Benedetta Vulcani ◽  
Bianca M. Poggianti ◽  
Rosita Paladino ◽  
Timothy Shimwell ◽  
...  
Keyword(s):  
Star Formation ◽  
Radio Emission ◽  
Formation Rate ◽  
Low Frequency ◽  
Stellar Disk ◽  
Gas Reservoirs ◽  
Very Large Array ◽  
Cluster Galaxies ◽  
Ram Pressure ◽  
The Galaxy

Abstract Ram pressure stripping is a crucial evolutionary driver for cluster galaxies. It is thought to be able to accelerate the evolution of their star formation, trigger the activity of their central active galactic nucleus (AGN) and the interplay between galactic and environmental gas, and eventually dissipate their gas reservoirs. We explored the outcomes of ram pressure stripping by studying the nonthermal radio emission of the jellyfish galaxy JW100 in the cluster A2626 (z = 0.055), by combining LOw Frequency Array, MeerKAT, and Very Large Array observations from 0.144 to 5.5 GHz. We studied the integrated spectra of the stellar disk, the stripped tail, and the AGN; mapped the spectral index over the galaxy; and constrained the magnetic field intensity to between 11 and 18 μG in the disk and <10 μG in the tail. The stellar disk radio emission is dominated by a radiatively old plasma, likely related to an older phase of a high star formation rate. This suggests that the star formation was quickly quenched by a factor of 4 in a few 107 yr. The radio emission in the tail is consistent with the stripping scenario, where the radio plasma that originally accelerated in the disk is subsequently displaced in the tail. The morphology of the radio and X-ray emissions supports the scenario of the accretion of magnetized environmental plasma onto the galaxy. The AGN nonthermal spectrum indicates that relativistic electron acceleration may have occurred simultaneously with a central ionized gas outflow, thus suggesting a physical connection between the two processes.

scholarly journals How Common are Engines in Ib/c Supernovae?

2005 ◽  
Vol 192 ◽  
pp. 425-429
Author(s):  
Edo Berger
Keyword(s):  
Radio Emission ◽  
Energy Input ◽  
Core Collapse ◽  
Large Array ◽  
Radio Observations ◽  
Large Reservoir ◽  
Very Large Array ◽  
Systematic Program ◽  
Variable Energy

SummaryThe association of γ-ray bursts (GRBs) and core-collapse supernovae (SNe) of Type Ib and Ic was motivated by the detection of SN 1998bw in the error box of GRB 980425 and the now-secure identification of a SN 1998bw-like event in the cosmological GRB 030329. The bright radio emission from SN 1998bw indicated that it possessed some of the unique attributes expected of GRBs, namely a large reservoir of energy in (mildly) relativistic ejecta and variable energy input. Here we discuss the results of a systematic program of radio observations of most reported Type Ib/c SNe accessible to the Very Large Array, designed to determine the fraction of Type Ib/c SNe driven by an engine. We conclude that: (i) the incidence of such events is low, < 3%, and (ii) there appears to be a clear dichotomy between the majority of hydrodynamic explosions (SNe) and engine-driven explosions (GRBs).

scholarly journals PS J1721+8842: A gravitationally lensed dual AGN system at redshift 2.37 with two radio components

2021 ◽  
Author(s):  
C S Mangat ◽  
J P McKean ◽  
R Brilenkov ◽  
P Hartley ◽  
H R Stacey ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
High Redshift ◽  
Galactic Nuclei ◽  
Host Galaxy ◽  
Very Large Array ◽  
The Hierarchical Structure ◽  
Black Hole Growth ◽  
Hole Growth ◽  
Array Imaging

Abstract Dual-Active Galactic Nuclei (AGN) are a natural consequence of the hierarchical structure formation scenario, and can provide an important test of various models for black hole growth. However, due to their rarity and difficulty to find at high redshift, very few confirmed dual-AGN are known at the epoch where galaxy formation peaks. Here we report the discovery of a gravitationally lensed dual-AGN system at redshift 2.37 comprising two optical/IR quasars separated by 6.5 ± 0.6 kpc, and a third compact (Reff = 0.45 ± 0.02 kpc) red galaxy that is offset from one of the quasars by 1.7 ± 0.1 kpc. From Very Large Array imaging at 3 GHz, we detect 600 and 340 pc-scale radio emission that is associated with both quasars. The 1.4 GHz luminosity densities of the radio sources are about 1024.35 W Hz−1, which is consistent with weak jets. However, the low brightness temperature of the emission is also consistent with star-formation at the level of 850 to 1150 M⊙ yr−1. Although this supports the scenario where the AGN and/or star-formation is being triggered through an ongoing triple-merger, a post-merger scenario where two black holes are recoiling is also possible, given that neither has a detected host galaxy.

scholarly journals COLDz: Probing Cosmic Star Formation With Radio Free–Free Emission

2022 ◽  
Vol 924 (2) ◽  
pp. 76
Author(s):  
Hiddo S. B. Algera ◽  
Jacqueline A. Hodge ◽  
Dominik A. Riechers ◽  
Sarah K. Leslie ◽  
Ian Smail ◽  
...  
Keyword(s):  
Star Formation ◽  
High Redshift ◽  
Formation Rate ◽  
Radio Spectrum ◽  
Star Formation History ◽  
Starburst Galaxy ◽  
Synchrotron Emission ◽  
Very Large Array ◽  
Star Forming ◽  
Order Of Magnitude

Abstract Radio free–free emission is considered to be one of the most reliable tracers of star formation in galaxies. However, as it constitutes the faintest part of the radio spectrum—being roughly an order of magnitude less luminous than radio synchrotron emission at the GHz frequencies typically targeted in radio surveys—the usage of free–free emission as a star formation rate tracer has mostly remained limited to the local universe. Here, we perform a multifrequency radio stacking analysis using deep Karl G. Jansky Very Large Array observations at 1.4, 3, 5, 10, and 34 GHz in the COSMOS and GOODS-North fields to probe free–free emission in typical galaxies at the peak of cosmic star formation. We find that z ∼ 0.5–3 star-forming galaxies exhibit radio emission at rest-frame frequencies of ∼65–90 GHz that is ∼1.5–2 times fainter than would be expected from a simple combination of free–free and synchrotron emission, as in the prototypical starburst galaxy M82. We interpret this as a deficit in high-frequency synchrotron emission, while the level of free–free emission is as expected from M82. We additionally provide the first constraints on the cosmic star formation history using free–free emission at 0.5 ≲ z ≲ 3, which are in good agreement with more established tracers at high redshift. In the future, deep multifrequency radio surveys will be crucial in order to accurately determine the shape of the radio spectrum of faint star-forming galaxies, and to further establish radio free–free emission as a tracer of high-redshift star formation.

scholarly journals The complete local volume groups sample – III. Characteristics of group central radio galaxies in the Local Universe

2019 ◽  
Vol 489 (2) ◽  
pp. 2488-2504 ◽  
Author(s):  
Konstantinos Kolokythas ◽  
Ewan O’Sullivan ◽  
Huib Intema ◽  
Somak Raychaudhury ◽  
Arif Babul ◽  
...  
Keyword(s):  
Black Hole ◽  
Radio Emission ◽  
Detection Rate ◽  
Very Large Array ◽  
Galaxy Groups ◽  
Local Volume ◽  
Radio Jets ◽  
Radio Detection ◽  
Wide Range ◽  
Poor Group

ABSTRACT Using new 610 and 235 MHz observations from the giant metrewave radio telescope (GMRT) in combination with archival GMRT and very large array (VLA) survey data, we present the radio properties of the dominant early-type galaxies in the low-richness subsample of the complete local-volume groups sample (CLoGS; 27 galaxy groups) and provide results for the radio properties of the full CLoGS sample for the first time. We find a high radio detection rate in the dominant galaxies of the low-richness subsample of 82 per cent (22/27); for the full CLoGS sample the detection rate is 87 per cent (46/53). The group-dominant galaxies exhibit a wide range of radio power, 1020–1025 W Hz−1 in the 235 and 610 MHz bands, with the majority (53 per cent) presenting point-like radio emission, 19 per cent hosting currently active radio jets, 6 per cent having remnant jets, 9 per cent being diffuse, and 13 per cent having no detected radio emission. The mean spectral index of the detected radio sources in the 235−610 MHz frequency range is found to be $\alpha _{235}^{610}\sim$0.68, and $\alpha _{235}^{1400}\sim$0.59 in the 235−1400 MHz one. In agreement with earlier studies, we find that the fraction of ultrasteep spectrum sources (α &gt; 1.3) is ∼4 per cent, mostly dependent on the detection limit at 235 MHz. The majority of point-like systems are found to reside in dynamically young groups, whereas jet systems show no preference between spiral-rich and spiral-poor group environments. The mechanical power of the jet sources in the low-richness sample groups is estimated to be ∼1042–1044 erg s−1 with their black hole masses ranging between 2 × 108 and 5 × 109 M⊙. We confirm previous findings that while radio jet sources tend to be associated with more massive black holes, black hole mass is not the decisive factor in determining jet activity or power.

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