scholarly journals High-Resolution Radio Observations of Five Optically Selected Type 2 Quasars

Symmetry ◽  
2020 ◽  
Vol 12 (4) ◽  
pp. 527
Author(s):  
Máté Krezinger ◽  
Sándor Frey ◽  
Zsolt Paragi ◽  
Roger Deane
Keyword(s):  
Structural Information ◽  
Galactic Nuclei ◽  
High Angular Resolution ◽  
Very Large Array ◽  
Long Baseline ◽  
Spectrum Radio ◽  
Sky Survey ◽  
5 Ghz ◽  
Symmetric Structures

Many low-luminosity active galactic nuclei (AGNs) contain a compact radio core which can be observed with high angular resolution using very long baseline interferometry (VLBI). Combining arcsec-scale structural information with milliarcsec-resolution VLBI imaging is a useful way to characterise the objects and to find compact cores on parsec scales. VLBI imaging could also be employed to look for dual AGNs when the sources show kpc-scale double symmetric structure with flat or inverted radio spectra. We observed five such sources at redshifts 0.36 < z < 0.58 taken from an optically selected sample of Type 2 quasars with the European VLBI Network (EVN) at 1.7 and 5 GHz. Out of the five sources, only one (SDSS J1026–0042) shows a confidently detected compact VLBI core at both frequencies. The other four sources are marginally detected at 1.7 GHz only, indicating resolved-out radio structure and steep spectra. Using first-epoch data from the ongoing Karl G. Jansky Very Large Array Sky Survey, we confirm that indeed all four of these sources have steep radio spectra on arcsec scale, contrary to the inverted spectra reported earlier in the literature. However, the VLBI-detected source, SDSS J1026−0042, has a flat integrated spectrum. Radio AGNs that show kpc-scale symmetric structures with truly flat or inverted spectra could still be promising candidates of dual AGNs, to be targeted with VLBI observations in the future.

scholarly journals Extragalactic megahertz-peaked spectrum radio sources at milliarcsecond scales

2019 ◽  
Vol 628 ◽  
pp. A56 ◽  
Author(s):  
M. A. Keim ◽  
J. R. Callingham ◽  
H. J. A. Röttgering
Keyword(s):  
Magnetic Field ◽  
Spectral Characteristics ◽  
Galactic Nuclei ◽  
Radio Sources ◽  
Long Baseline ◽  
Spectrum Radio ◽  
Spectral Peaks ◽  
Murchison Widefield Array ◽  
Very Long Baseline Array ◽  
Field Strengths

Extragalactic peaked-spectrum radio sources are thought to be the progenitors of larger, radio-loud active galactic nuclei (AGN). Synchrotron self-absorption (SSA) has often been identified as the cause of their spectral peak. The identification of new megahertz-peaked spectrum sources from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey provides an opportunity to test how radio sources with spectral peaks below 1 GHz fit within this evolutionary picture. We observed six peaked-spectrum sources selected from the GLEAM survey, three that have spectral characteristics which violate SSA and three that have spectral peaks below 230 MHz, with the Very Long Baseline Array at 1.55 and 4.96 GHz. We present milliarcsecond resolution images of each source and constrain their morphology, linear size, luminosity, and magnetic field strength. Of the sources that are resolved by our study, the sources that violate SSA appear to be compact doubles, while the sources with peak frequencies below 230 MHz have core-jet features. We find that all of our sources are smaller than expected from SSA by factors of ≳20. We also find that component magnetic field strengths calculated from SSA are likely inaccurate, differing by factors of ≳5 from equipartition estimates. The calculated equipartition magnetic field strengths more closely resemble estimates from previously studied gigahertz-peaked spectrum sources. Exploring a model of the interaction between jets and the interstellar medium, we demonstrate that free-free absorption (FFA) can accurately describe the linear sizes and peak frequencies of our sources. Our findings support the theory that there is a fraction of peaked-spectrum sources whose spectral peaks are best modeled by FFA, implying our understanding of the early stages of radio AGN is incomplete.

scholarly journals Frequency Dependence of the Parsec-scale Polarization Structures of BL Lac Objects

2001 ◽  
Vol 205 ◽  
pp. 140-141
Author(s):  
A.B. Pushkarev ◽  
D.C. Gabuzda ◽  
T.V. Cawthorne
Keyword(s):  
Line Emission ◽  
Galactic Nuclei ◽  
Optical Emission ◽  
Bl Lac Objects ◽  
Bl Lacertae ◽  
Sky Survey ◽  
Radiation Sources ◽  
Wide Wavelength Range ◽  
Bl Lac ◽  
5 Ghz

BL Lacertae objects are active galactic nuclei with weak or undetectable line emission and strong variability in total intensity and linear polarization over a wide wavelength range from optical to radio. The radio emission and much of the optical emission is believed to be synchrotron radiation. Sources in the complete sample of BL Lac objects defined by Kühr and Schmidt (1990) have: 5 GHz fluxes of at least 1 Jy, radio spectral index α ≥ −0.5 (Sv ˜ v+α), rest frame equivalent width of the strongest emission lines less than 5 Å, and optical counterparts on the Sky Survey plates with brightness greater than 20m.

scholarly journals Evidence for obscured broad [O iii] components in Type-2 AGN

2021 ◽  
Vol 502 (2) ◽  
pp. 2508-2512
Author(s):  
Xue-Guang Zhang
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Unified Model ◽  
Sloan Digital Sky Survey ◽  
The Core ◽  
Large Samples ◽  
Sky Survey ◽  
Narrow Emission

ABSTRACT In the manuscript, we report evidence on broad [O iii] components apparently obscured in Type-2 active galactic nuclei (AGN) under the framework of the unified model, after checking properties of broad [O iii] emissions in large samples of Type-1 and Type-2 AGN in Sloan Digital Sky Survey DR12. We can well confirm the statistically lower flux ratios of the broad to the core [O iii] components in Type-2 AGN than in Type-1 AGN, which can be naturally explained by stronger obscured broad [O iii] components by central dust torus in Type-2 AGN, unless the unified model for AGN was not appropriate to the narrow emission lines. The results provide further evidence to support broad [O iii] components coming from emission regions nearer to central BHs, and also indicate the core [O iii] component as the better indicator for central activities in Type-2 AGN, due to few effects of obscuration on the core [O iii] component. Considering the broad [O iii] components as signs of central outflows, the results provide evidence for strong central outflows being preferentially obscured in Type-2 AGN. Furthermore, the obscured broad [O iii] component can be applied to explain the different flux ratios of [O iii]λ5007Å/H β between Type-1 and Type-2 AGN in the BPT diagram.

scholarly journals Variable radio AGN at high redshift identified in the VLA Sky Survey

2020 ◽  
Vol 15 (S359) ◽  
pp. 27-32
Author(s):  
Kristina Nyland ◽  
Dillon Dong ◽  
Pallavi Patil ◽  
Mark Lacy ◽  
Amy Kimball ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
High Redshift ◽  
Galactic Nuclei ◽  
Very Large Array ◽  
The Past ◽  
Sky Survey ◽  
Upper Limits ◽  
Radio Transients ◽  
Variable Radio

AbstractAs part of an on-going study of radio transients in Epoch 1 (2017–2019) of the Very Large Array Sky Survey (VLASS), we have discovered a sample of 0.2 < z < 3.2 active galactic nuclei (AGN) selected in the optical/infrared that have recently brightened dramatically in the radio. These sources would have previously been classified as radio-quiet based on upper limits from the Faint Images of the Radio Sky at Twenty-centimeters (FIRST; 1993-2011) survey; however, they are now consistent with radio-loud quasars. We present a quasi-simultaneous, multi-band (1–18 GHz) VLA follow-up campaign of our sample of AGN with extreme radio variability. We conclude that the radio properties are most consistent with AGN that have recently launched jets within the past few decades, potentially making them among the youngest radio AGN known.

scholarly journals A compact core-jet structure in the changing-look Seyfert NGC 2617

2021 ◽  
Vol 503 (3) ◽  
pp. 3886-3895
Author(s):  
Jun Yang ◽  
Zsolt Paragi ◽  
Robert J Beswick ◽  
Wen Chen ◽  
Ilse M van Bemmel ◽  
...  
Keyword(s):  
Galactic Nuclei ◽  
Optical Emission ◽  
Very Large Array ◽  
The North ◽  
Long Baseline ◽  
Type Change ◽  
Very Long Baseline Array ◽  
Jet Structure ◽  
Seyfert Type ◽  
Inside Out

ABSTRACT The nearby face-on spiral galaxy NGC 2617 underwent an unambiguous ‘inside–out’ multiwavelength outburst in Spring 2013, and a dramatic Seyfert-type change probably between 2010 and 2012, with the emergence of broad optical emission lines. To search for the jet activity associated with this variable accretion activity, we carried out multiresolution and multiwavelength radio observations. Using the very long baseline interferometric (VLBI) observations with the European VLBI Network at 1.7 and 5.0 GHz, we find that NGC 2617 shows a partially synchrotron self-absorbed compact radio core with a significant core shift, and an optically thin steep-spectrum jet extending towards the north up to about 2 pc in projection. We also observed NGC 2617 with the electronic Multi-Element Remotely Linked Interferometer Network at 1.5 and 5.5 GHz, and revisited the archival data of the Very Large Array (VLA) and the Very Long Baseline Array (VLBA). The radio core had a stable flux density of ∼1.4 mJy at 5.0 GHz between 2013 June and 2014 January, in agreement with the expectation of a supermassive black hole in the low accretion rate state. The northern jet component is unlikely to be associated with the ‘inside–out’ outburst of 2013. Moreover, we report that most optically selected changing-look active galactic nuclei (AGN) at z &lt; 0.83 are sub-mJy radio sources in the existing VLA surveys at 1.4 GHz, and it is unlikely that they are more active than normal AGN at radio frequencies.

scholarly journals Local AGN survey (LASr): I. Galaxy sample, infrared colour selection, and predictions for AGN within 100 Mpc

2020 ◽  
Vol 494 (2) ◽  
pp. 1784-1816
Author(s):  
D Asmus ◽  
C L Greenwell ◽  
P Gandhi ◽  
P G Boorman ◽  
J Aird ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Galaxy Evolution ◽  
Galactic Nuclei ◽  
Wide Field ◽  
X Ray ◽  
Sky Survey ◽  
Galaxy Sample ◽  
Redshift Survey ◽  
Infrared Survey

ABSTRACT To answer major questions on supermassive black hole (SMBH) and galaxy evolution, a complete census of SMBH growth, i.e. active galactic nuclei (AGN), is required. Thanks to all-sky surveys by the Wide-field Infrared Survey Explorer (WISE) and the Spectrum-Roentgen-Gamma (SRG) missions, this task is now feasible in the nearby Universe. We present a new survey, the Local AGN Survey (LASr), with the goal of identifying AGN unbiased against obscuration and determining the intrinsic Compton-thick (CT) fraction. We construct the most complete all-sky galaxy sample within 100 Mpc ($90{{\ \rm per\ cent}}$ completeness for log (M*/M⊙) ∼ 9.4), four times deeper than the current reference, the Two Micron All-Sky Survey Redshift Survey (2MRS), which misses ${\sim}20{{\ \rm per\ cent}}$ of known luminous AGN. These 49k galaxies serve as parent sample for LASr, called LASr-GPS. It contains 4.3k already known AGN, $\ge 82{{\ \rm per\ cent}}$ of these are estimated to have $L^\mathrm{nuc}(12\, \mu \mathrm{m})\lt 10^{42.3}$ erg s−1, i.e. are low-luminosity AGN. As a first method for identifying Seyfert-like AGN, we use WISE-based infrared colours, finding 221 galaxies at $L^\mathrm{nuc}(12\, \mu \mathrm{m})\ge 10^{42.3}$ erg s−1 to host an AGN at $90{{\ \rm per\ cent}}$ reliability. This includes 61 new AGN candidates and implies an optical type 2 fraction of 50–71 per cent. We quantify the efficiency of this technique and estimate the total number of AGN with $L^\mathrm{int}(\rm {2-10\,keV})\ge 10^{42}$ erg s−1 in the volume to be $362^{+145}_{-116}$ ($8.6^{+3.5}_{-2.8}\, \times$ 10−5 Mpc−3). X-ray brightness estimates indicate the CT fraction to be 40–55 per cent to explain the Swift non-detections of the infrared selected objects. One third of the AGN within 100 Mpc remain to be identified, and we discuss the prospects for the eROSITA all-sky survey to detect them.

scholarly journals Radio Structure of Seyfert Galaxies

1980 ◽  
Vol 92 ◽  
pp. 161-163
Author(s):  
A. S. Wilson ◽  
A. G. Willis
Keyword(s):  
Radio Source ◽  
Structural Information ◽  
Minimum Energy ◽  
Close Relation ◽  
Seyfert Galaxies ◽  
Very Large Array ◽  
Line Region ◽  
Double Radio Source ◽  
Optical Continuum ◽  
5 Ghz

We have recently mapped about a dozen Seyfert galaxies with the Very Large Array at 5 GHz and obtained less complete structural information on about a dozen more. Most sources are heavily resolved at resolutions near or below 1 arc sec, with linear scales in the range several hundred parsecs to a few kiloparsecs. For 3 galaxies (Mark 3, NGC 1068 and NGC 5548) the structure is double with two components more or less symmetrically placed on opposite sides of the optical nucleus. A third component, when present, coincides with the optical nucleus. This result provides strong evidence that “double radio source machines” also reside in the nuclei of active spiral galaxies as well as ellipticals. Other sources show a more diffuse morphology, but usually also possess a compact radio source associated with the optical continuum nucleus. A close relation between the extended radio emission and the thermal gas in the forbidden line region is indicated since (a) they have similar extents, (b) the radio and forbidden line powers are correlated, (c) the relativistic plus magnetic (B2eq/4π) and thermal pressures (nekTe) are similar and (d) the kinetic energy of the thermal gas and the minimum energy for synchrotron radiation are comparable. For the double sources, the radio emitting plasma is probably ejected from the compact nucleus and slowed by the large quantities of thermal gas in the forbidden line region. Alternatively, radio sources with more diffuse morphology may derive their luminosity from cosmic rays accelerated “in situ” by shock waves associated with the high velocity thermal gas and a magnetic field from a compressed (accreted?) interstellar medium.

scholarly journals The VSOP project: Space VLBI Imaging of AGN at 1.6 and 5 GHz

2001 ◽  
Vol 205 ◽  
pp. 118-121
Author(s):  
Y. Murata ◽  
H. Hirabayashi ◽  
P.G. Edwards
Keyword(s):  
Active Galactic Nuclei ◽  
Very Long Baseline Interferometry ◽  
Galactic Nuclei ◽  
Radio Telescopes ◽  
Space Observatory ◽  
Long Baseline ◽  
5 Ghz

The VLBI Space Observatory Programme (VSOP) combines an orbiting radiotelescope with arrays of ground radio telescopes to extend the Very Long Baseline Interferometry (VLBI) technique to baselines up to almost three Earth diameters. In this paper, we present results from VSOP observations of active galactic nuclei (AGN) at 1.6 and 5 GHz from the first 3.5 years of the mission.

Magnetic Fields in the Relativistic Jets of Active Galactic Nuclei

2018 ◽  
Vol 14 (S342) ◽  
pp. 189-196
Author(s):  
Denise C. Gabuzda
Keyword(s):  
Active Galactic Nuclei ◽  
Very Long Baseline Interferometry ◽  
Galactic Nuclei ◽  
Outward Current ◽  
Relativistic Jets ◽  
Local Effects ◽  
Very Large Array ◽  
Long Baseline ◽  
Wide Range ◽  
Jet Axis

AbstractAn abundance of information about the magnetic (B) fields of relativistic AGN jets has been obtained through radio polarization observations made on a wide range of scales, from the parsec scales probed by Very Long Baseline Interferometry to the kiloparsec scales probed by instruments such as the the Jansky Very Large Array and e-MERLIN. The observed radio emission is synchrotron radiation, for which the linear polarization angles in optically thin regions is orthogonal to the local synchrotron B fields. The characteristic B field structures observed for these jets on parsec scales are described. A key question is whether B field structures observed in particular AGN jets come about primarily due to “global” effects such as the intrinsic B field of the jet itself, which is expected to be helical, or local phenomena such as shocks, shear and bending of the jets. Observational criteria that can be used to try to distinguish between various possible origins for observed B field structures are described. There is now considerable evidence that the relativistic jets of AGNs do indeed carry helical B fields, with the observed polarization also sometimes appreciably influenced by local effects. Patterns seen in the helical B field components, indicated for example by Faraday rotation observations, provide unique information about the processes involved in the generation of these helical B fields. The collected observations on parsec and kiloparsec scales provide weighty evidence that an important role is played by the action of a cosmic “battery” that acts to generate an inward current along the jet axis and an outward current in a more extended region surrounding the jet.

scholarly journals Feedback from low-luminosity radio galaxies: B2 0258+35

2019 ◽  
Vol 629 ◽  
pp. A58 ◽  
Author(s):  
Suma Murthy ◽  
Raffaella Morganti ◽  
Tom Oosterloo ◽  
Robert Schulz ◽  
Dipanjan Mukherjee ◽  
...  
Keyword(s):  
Radio Source ◽  
Surrounding Medium ◽  
Galactic Nuclei ◽  
Molecular Gas ◽  
Very Large Array ◽  
Radio Jets ◽  
Shock Heating ◽  
Spectrum Radio ◽  
The Galaxy ◽  
Early Type Galaxy

Low-luminosity radio-loud active galactic nuclei (AGN) are of importance in studies concerning feedback from radio AGN since a dominant fraction of AGN belong to this class. We report high-resolution Very Large Array (VLA) and European VLBI Network (EVN) observations of H I 21 cm absorption from a young, compact steep-spectrum radio source, B2 0258+35, nested in the early-type galaxy NGC 1167, which contains a 160 kpc H I disc. Our VLA and EVN H I absorption observations, modelling, and comparison with molecular gas data suggest that the cold gas in the centre of NGC 1167 is very turbulent (with a velocity dispersion of ∼90 km s−1) and that this turbulence is induced by the interaction of the jets with the interstellar medium (ISM). Furthermore, the ionised gas in the galaxy shows evidence of shock heating at a few kpc from the radio source. These findings support the results from numerical simulations of radio jets expanding into a clumpy gas disc, which predict that the radio jets in this case percolate through the gas disc and drive shocks into the ISM at distances much larger than their physical extent. These results expand the number of low-luminosity radio sources found to impact the surrounding medium, thereby highlighting the possible relevance of these AGN for feedback.

Sign in / Sign up

Export Citation Format

Share Document