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-emitting narrow-line Seyfert 1 galaxies in the JVLA perspective

2018 ◽  
Vol 614 ◽  
pp. A87 ◽  
Author(s):  
M. Berton ◽  
E. Congiu ◽  
E. Järvelä ◽  
R. Antonucci ◽  
P. Kharb ◽  
...  
Keyword(s):  
Radio Continuum ◽  
Large Array ◽  
Narrow Line ◽  
Diffuse Emission ◽  
Parent Population ◽  
Very Large Array ◽  
General Properties ◽  
Spectrum Radio ◽  
First Results ◽  
5 Ghz

We report the first results of a survey on 74 narrow-line Seyfert 1 galaxies (NLS1s) carried out in 2015 with the Karl G. Jansky Very Large Array (JVLA) at 5 GHz in A-configuration. So far, this is the largest survey aimed to image the radio continuum of NLS1s. We produced radio maps in order to compare the general properties of three different samples of objects: radio-quiet NLS1s (RQNLS1s), steep-spectrum radio-loud NLS1s (S-NLS1s), and flat-spectrum radio-loud NLS1s (F-NLS1s). We find that the three classes correspond to different radio morphologies, with F-NLS1s being more compact, and RQNLS1s often showing diffuse emission on kpc scales. We also find that F-NLS1s might be low-luminosity and possibly young blazars, and that S-NLS1s are part of the parent population of F-NLS1s. Dedicated studies to RQNLS1s are needed to fully understand their role in the unification pictures.

scholarly journals Absorbed relativistic jets in radio-quiet narrow-line Seyfert 1 galaxies

2020 ◽  
Vol 636 ◽  
pp. A64
Author(s):  
M. Berton ◽  
E. Järvelä ◽  
L. Crepaldi ◽  
A. Lähteenmäki ◽  
M. Tornikoski ◽  
...  
Keyword(s):  
Radio Emission ◽  
Active Galactic Nuclei ◽  
High Frequency ◽  
Galactic Nuclei ◽  
Large Array ◽  
Narrow Line ◽  
Relativistic Jets ◽  
Ionized Gas ◽  
Very Large Array ◽  
Relativistic Jet

Narrow-line Seyfert 1 (NLS1) galaxies are peculiar active galactic nuclei. Most of them do not show strong radio emission, but seven radio-quiet (or radio-silent) NLS1s have recently been detected flaring multiple times at 37 GHz by the Metsähovi Radio Telescope, indicating relativistic jets in these peculiar sources. We observed them with the Karl G. Jansky Very Large Array (JVLA) in A configuration at 1.6, 5.2, and 9.0 GHz. Our results show that these sources are either extremely faint or not detected in the JVLA bands. At these frequencies, the radio emission from their relativistic jet must be absorbed, either through synchrotron self-absorption as it occurs in gigahertz-peaked sources, or more likely, through free-free absorption by a screen of ionized gas associated with starburst activity or shocks. Our findings cast new shadows on the radio-loudness criterion, which seems to be increasingly frequently a misleading parameter. New high-frequency and high-resolution radio observations are essential to test our hypotheses.

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.

VLA Observations of a Sample of Low-Brightness 6.7 GHz Methanol Masers

2017 ◽  
Vol 13 (S336) ◽  
pp. 311-312
Author(s):  
Luca Olmi ◽  
Esteban D. Araya ◽  
Jason Armstrong
Keyword(s):  
New Mexico ◽  
Star Formation ◽  
Far Infrared ◽  
Large Array ◽  
Very Large Array ◽  
Early Stages ◽  
Methanol Masers ◽  
Infrared Sources ◽  
Massive Cores

AbstractIn 2014 we conducted a survey for 6.7 GHz methanol masers with the Arecibo Telescope toward far infrared sources selected from the Hi-GAL catalog of massive cores. We found a number of sources with weak 6.7 GHz methanol masers, possibly indicating regions in early stages of star formation. Here we describe the results of follow-up observations that were conducted with the Very Large Array in New Mexico to characterize this new population of “weak” 6.7 GHz methanol masers.

scholarly journals Accuracy Assessment of Hipparcos Optical and VLA Radio Positions of Stars

1993 ◽  
Vol 156 ◽  
pp. 377-380
Author(s):  
H. G. Walter ◽  
R. Hering ◽  
H. Lenhardt ◽  
Chr. deVegt ◽  
D.R. Florkowski ◽  
...  
Keyword(s):  
Radio Emission ◽  
Reference Frame ◽  
Accuracy Assessment ◽  
Optical Emission ◽  
Relative Orientation ◽  
Large Array ◽  
Proper Motions ◽  
Data Noise ◽  
Very Large Array ◽  
Radio Stars

Optical positions of some 30 radio stars derived from 12 months of HIPPARCOS measurements are compared with their radio positions obtained with the Very Large Array (VLA). — Once the lengths of arcs between optical and radio positions of pairs of stars are calculated the differences of the arcs are formed. They provide an estimate of the coincidence of the optical and radio emission centres. — From the comparison of optical and radio positions infinitesimal rotation angles of the HIPPARCOS frame with respect to the VLA extragalactic reference frame are determined by rigid rotations. After taking account of the relative orientation of the frames the standard deviations of the remaining residuals are approximately of the order of the VLA observation errors, thus demonstrating the reliability of the HIPPARCOS results. However, they also indicate some data noise very likely caused by the low accuracy of optical proper motions used to bridge the HIPPARCOS-radio epoch differences up to 9 years, and possible discrepancies of radio-optical emission centres of some stars.

AGN Feedback and its Importance to Galaxy Evolution in the Era of the ngVLA

2018 ◽  
Vol 14 (A30) ◽  
pp. 78-81
Author(s):  
Kristina Nyland
Keyword(s):  
Star Formation ◽  
Active Galactic Nuclei ◽  
Galaxy Evolution ◽  
Angular Resolution ◽  
Galactic Nuclei ◽  
Gas Content ◽  
Large Array ◽  
Very Large Array ◽  
Frequency Coverage ◽  
Evolutionary Role

AbstractEnergetic feedback by Active Galactic Nuclei (AGN) plays an important evolutionary role in the regulation of star formation (SF) on galactic scales. However, the effects of this feedback as a function of redshift and galaxy properties such as mass, environment and cold gas content remain poorly understood. The broad frequency coverage (1 to 116 GHz), high collecting area (about ten times higher than the Karl G. Jansky Very Large Array), and superb angular resolution (maximum baselines of at least a few hundred km) of the proposed next-generation Very Large Array (ngVLA) are uniquely poised to revolutionize our understanding of AGN and their role in galaxy evolution.

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 A Pilot Radio Search for Magnetic Activity in Directly Imaged Exoplanets

2021 ◽  
Vol 163 (1) ◽  
pp. 15
Author(s):  
Y. Cendes ◽  
P. K. G. Williams ◽  
E. Berger
Keyword(s):  
Pilot Study ◽  
Radio Emission ◽  
Angular Resolution ◽  
Magnetic Activity ◽  
Systematic Search ◽  
Archival Data ◽  
Large Array ◽  
Very Large Array ◽  
Upper Limits ◽  
Host Stars

Abstract We present the first systematic search for GHz frequency radio emission from directly imaged exoplanets using Very Large Array observations of sufficient angular resolution to separate the planets from their host stars. We obtained results for five systems and eight exoplanets located at ≲50 pc through new observations (Ross 458, GU Psc, and 51 Eri) and archival data (GJ 504 and HR 8799). We do not detect radio emission from any of the exoplanets, with 3σ luminosity upper limits of (0.9–23) × 1021 erg s−1. These limits are comparable to the level of radio emission detected in several ultracool dwarfs, including T dwarfs, whose masses are only a factor of two times higher than those of the directly imaged exoplanets. Despite the lack of detections in this pilot study, we highlight the need for continued GHz frequency radio observations of nearby exoplanets at μJy-level sensitivity.

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