scholarly journals A multiwavelength study of the dual nuclei in Mrk 212

2020 ◽  
Vol 500 (3) ◽  
pp. 3908-3919
Author(s):  
K Rubinur ◽  
P Kharb ◽  
M Das ◽  
P T Rahna ◽  
M Honey ◽  
...  
Keyword(s):  
Radio Source ◽  
Galactic Nuclei ◽  
Optical Emission ◽  
Radio Observations ◽  
Radio Structure ◽  
Very Large Array ◽  
Extended Radio ◽  
The Galaxy ◽  
Double Radio Source ◽  
Tidal Tails

ABSTRACT We present radio observations of the galaxy merger remnant Mrk 212 with the Karl G. Jansky Very Large Array (VLA) and the upgraded Giant Meter Radio Telescope (uGMRT). Mrk 212 has two previously known radio sources associated with the two optical nuclei, S1 and S2, with a projected separation of ∼6 kpc, making it a dual active galactic nuclei (AGN) candidate. Our new 15-GHz VLA observations reveal that S1 is a double radio source centred around the optical nucleus; its total extent is ∼750 pc its average 1.4−8.5 GHz spectral index is −0.81 ± 0.06. S1 therefore resembles a compact symmetric object. The 15-GHz VLA image identifies the radio source at S2 to be a compact core. Our radio observations therefore strongly support the presence of a dual AGN in Mrk 212. The optical emission line flux ratios obtained from the Himalayan Chandra Telescope (HCT) observations however, show that S1 and S2 both fall in the AGN + star formation (SF) region of the Baldwin, Philips and Terlevich (BPT) diagram. Weak AGN lying in the SF or AGN + SF intermediate regions in the BPT diagram have indeed been reported in the literature; our sources clearly fall in the same category. We find an extended radio structure in our newly reduced 8.5-GHz-VLA data, that is offset by ∼1 arcsec from the optical nucleus S2. New deep FUV and NUV observations with the Ultraviolet Imaging Telescope aboard AstroSat reveal SF knots around S2 as well as kpc-scale tidal tails; the SF knots around S2 coincide with the extended radio structure detected at 8.5 GHz. The radio spectral indices are consistent with SF. Any possible association with the AGN in S2 is unclear at this stage.

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.

scholarly journals Radio Continuum Emission from the Nuclei of Normal Galaxies

1980 ◽  
Vol 5 ◽  
pp. 177-184 ◽  
Author(s):  
J. M. van der Hulst
Keyword(s):  
Radio Emission ◽  
Galactic Center ◽  
Galactic Nuclei ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Thermal Source ◽  
Very Large Array ◽  
Normal Galaxies ◽  
The Galaxy ◽  
Sgr A

During the last few years detailed and sensitive observations of the radio emission from the nuclei of many normal spiral galaxies has become available. Observations from the Very Large Array (VLA) of the National Radio Astronomy Observatory (NRAO1), in particular, enable us to distinguish details on a scale of ≤100 pc for galaxies at distances less than 21 Mpc. The best studied nucleus, however, still is the center of our own Galaxy (see Oort 1977 and references therein). Its radio structure is complex. It consists of an extended non-thermal component 200 × 70 pc in size, with embedded therein several giant HII regions and the central source Sgr A (˜9 pc in size). Sgr A itself consists of a thermal source, Sgr A West, located at the center of the Galaxy, and a weaker, non-thermal source, Sgr A East. Sgr A West moreover contains a weak, extremely compact (≤10 AU) source. The radio morphology of several other galactic nuclei is quite similar to that of the Galactic Center, as will be discussed in section 2. Recent reviews of the radio properties of the nuclei of normal galaxies have been given by Ekers (1978a,b) and De Bruyn (1978). The latter author, however, concentrates on galaxies with either active nuclei or an unusual radio morphology. In this paper I will describe recent results from the Westerbork Synthesis Radio Telescope (WSRT, Hummel 1979), the NRAO 3-element interferometer (Carlson, 1977; Condon and Dressel 1978), and the VLA (Heckman et al., 1979; Van der Hulst et al., 1979). I will discuss the nuclear radio morphology in section 2, the luminosities in section 3, and the spectra in section 4. In section 5 I will briefly comment upon the possible implications for the physical processes in the nuclei that are responsible for the radio emission.

scholarly journals Ultra-steep spectrum emission in the merging galaxy cluster Abell 1914

2019 ◽  
Vol 622 ◽  
pp. A22 ◽  
Author(s):  
S. Mandal ◽  
H. T. Intema ◽  
T. W. Shimwell ◽  
R. J. van Weeren ◽  
A. Botteon ◽  
...  
Keyword(s):  
Low Frequency ◽  
Galaxy Cluster ◽  
Diffuse Emission ◽  
Radio Observations ◽  
Very Large Array ◽  
Radio Halo ◽  
The Galaxy ◽  
Distinct Source ◽  
Relativistic Particles ◽  
Massive Galaxy

A number of radio observations have revealed the presence of large synchrotron-emitting sources associated with the intra-cluster medium. There is strong observational evidence that the emitting particles have been (re-)accelerated by shocks and turbulence generated during merger events. The particles that are accelerated are thought to have higher initial energies than those in the thermal pool but the origin of such mildly relativistic particles remains uncertain and needs to be further investigated. The galaxy cluster Abell 1914 is a massive galaxy cluster in which X-ray observations show clear evidence of merging activity. We carried out radio observations of this cluster with the LOw Frequency ARay (LOFAR) at 150 MHz and the Giant Metrewave Radio Telescope (GMRT) at 610 MHz. We also analysed Very Large Array (VLA) 1.4 GHz data, archival GMRT 325 MHz data, CFHT weak lensing data and Chandra observations. Our analysis shows that the ultra-steep spectrum source (4C38.39; α ≲ −2), previously thought to be part of a radio halo, is a distinct source with properties that are consistent with revived fossil plasma sources. Finally, we detect some diffuse emission to the west of the source 4C38.39 that could belong to a radio halo.

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 < 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 Mergers trigger active galactic nuclei out to z ∼ 0.6

2020 ◽  
Vol 637 ◽  
pp. A94 ◽  
Author(s):  
F. Gao ◽  
L. Wang ◽  
W. J. Pearson ◽  
Y. A. Gordon ◽  
B. W. Holwerda ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
High Redshift ◽  
Galactic Nuclei ◽  
Optical Emission ◽  
Sloan Digital Sky Survey ◽  
Positive Trend ◽  
Host Galaxies ◽  
Massive Galaxies ◽  
The Galaxy ◽  
Mass Assembly

Aims. The fueling and feedback of active galactic nuclei (AGNs) are important for understanding the co-evolution between black holes and host galaxies. Mergers are thought to have the capability to bring gas inward and ignite nuclear activity, especially for more powerful AGNs. However, there is still significant ongoing debate on whether mergers can trigger AGNs and, if they do, whether mergers are a significant triggering mechanism. Methods. We selected a low-redshift (0.005 <  z <  0.1) sample from the Sloan Digital Sky Survey and a high-redshift (0 <  z <  0.6) sample from the Galaxy And Mass Assembly survey. We took advantage of the convolutional neural network technique to identify mergers. We used mid-infrared (MIR) color cut and optical emission line diagnostics to classify AGNs. We also included low excitation radio galaxies (LERGs) to investigate the connection between mergers and low accretion rate AGNs. Results. We find that AGNs are more likely to be found in mergers than non-mergers, with an AGN excess up to 1.81 ± 0.16, suggesting that mergers can trigger AGNs. We also find that the fraction of mergers in AGNs is higher than that in non-AGN controls, for both MIR and optically selected AGNs, as well as LERGs, with values between 16.40 ± 0.5% and 39.23 ± 2.10%, implying a non-negligible to potentially significant role of mergers in triggering AGNs. This merger fraction in AGNs increases as stellar mass increases, which supports the idea that mergers are more important for triggering AGNs in more massive galaxies. In terms of merger fraction as a function of AGN power we find a positive trend for MIR selected AGNs and a complex trend for optically selected AGNs, which we interpret under an evolutionary scenario proposed by previous studies. In addition, obscured MIR selected AGNs are more likely to be hosted in mergers than unobscured MIR selected AGNs.

Optical Emission from the Extended Radio Source 3C277.3 = Coma-A

1981 ◽  
Vol 247 ◽  
pp. L5 ◽  
Author(s):  
G. K. Miley ◽  
T. M. Heckman ◽  
H. R. Butcher ◽  
W. J. M. van Breugel
Keyword(s):  
Radio Source ◽  
Optical Emission ◽  
Extended Radio ◽  
Extended Radio Source

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 Strong Magnetic Field Galactic Center-AGN-Quasar Model

1989 ◽  
Vol 136 ◽  
pp. 335-340 ◽  
Author(s):  
Howard D. Greyber
Keyword(s):  
Magnetic Field ◽  
Strong Magnetic Field ◽  
Galactic Center ◽  
Galactic Disk ◽  
Galactic Nuclei ◽  
Current Loop ◽  
Toroidal Plasma ◽  
Extended Radio ◽  
The Galaxy ◽  
Magnetic Field Model

The energy storage and dynamics at the center of galaxies is explained using a new construct, the gravitationally bound current loop (GBCL), produced when the galaxy formed under gravitational collapse. Thin toroidal plasma around the slender intense relativistic current loop is bound to it by the Maxwell “frozen-field” condition, and also binds gravitationally to the central object (presumably a black hole). The Strong Magnetic Field model (SMF) explains directly the Milky Way (MW) galactic center radio observations of a vertical magnetic field perpendicular to the galactic disk and the extended radio arcs, as well as the production of successive radio blobs ejected from the compact cores of active galactic nuclei (AGN) or quasars.

scholarly journals Distant Radio Galaxies: the Strong Link between the Radio and Optical Emission

1996 ◽  
Vol 175 ◽  
pp. 583-584
Author(s):  
Huub Röttgering
Keyword(s):  
Radio Source ◽  
Line Emission ◽  
Optical Emission ◽  
Radio Galaxies ◽  
Radio Sources ◽  
Strong Link ◽  
The Galaxy ◽  
Optical Continuum

Recent observations of distant radio galaxies show that there is a strong link between the radio source and the optical continuum and Lyα line emission from the galaxy. This link is discussed in terms of differences in age, orientation and environment between the radio sources.

scholarly journals Rotating Gas and the Shapes of Radio Sources

1982 ◽  
Vol 97 ◽  
pp. 25-26
Author(s):  
L. S. Sparke
Keyword(s):  
Seyfert Galaxies ◽  
External Pressure ◽  
Opening Angle ◽  
Radio Sources ◽  
Extragalactic Radio Source ◽  
Radio Structure ◽  
Radio Jets ◽  
Extended Radio ◽  
The Galaxy ◽  
Scale Properties

The power for a strong extragalactic radio source comes from deep within the nucleus, but the extended radio structure is clearly related to the larger-scale properties of the galaxy in which it lives. Very large sources are found in elliptical rather than spiral galaxies, and big galaxies have stronger radio sources than small ones. The narrow jets mapped in weaker radio galaxies do not expand with a constant opening angle, but become better focussed along their length, suggesting that they are confined by an external pressure. This paper discusses how the rotation of a radio galaxy affects the distribution of gas within it, and consequently the radio structure in elliptical and Seyfert galaxies. A model is proposed which leads to a specific prediction, relating the width of radio jets to the rotation speed of the galaxy in which they lie.

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