scholarly journals Quasars and active galactic nuclei: high resolution radio imaging.

1995 ◽  
Vol 92 (25) ◽  
pp. 11339-11341 ◽  
Author(s):  
M. H. Cohen ◽  
K. I. Kellermann
2018 ◽  
Vol 618 ◽  
pp. A68 ◽  
Author(s):  
S. Frey ◽  
O. Titov ◽  
A. E. Melnikov ◽  
P. de Vicente ◽  
F. Shu

Context. Radio-loud active galactic nuclei in the early Universe are rare. The quasars J0906+6930 at redshift z = 5.47 and J2102+6015 at z = 4.57 stand out from the known sample with their compact emission on milliarcsecond (mas) angular scale with high (0.1 Jy level) flux densities measured at GHz radio frequencies. This makes them ideal targets for very long baseline interferometry (VLBI) observations. Aims. By means of VLBI imaging we can reveal the inner radio structure of quasars and model their brightness distribution to better understand the geometry of the jet and the physics of the sources. Methods. We present sensitive high-resolution VLBI images of J0906+6930 and J2102+6015 at two observing frequencies, 2.3 and 8.6 GHz. The data were taken in an astrometric observing programme involving a global five-element radio telescope array. We combined the data from five different epochs from 2017 February to August. Results. For one of the highest redshift blazars known, J0906+6930, we present the first-ever VLBI image obtained at a frequency below 8 GHz. Based on our images at 2.3 and 8.6 GHz, we confirm that this source has a sharply bent helical inner jet structure within ∼3 mas from the core. The quasar J2102+6015 shows an elongated radio structure in the east–west direction within the innermost ∼2 mas that can be described with a symmetric three-component brightness distribution model at 8.6 GHz. Because of their non-pointlike mas-scale structure, these sources are not ideal as astrometric reference objects. Our results demonstrate that VLBI observing programmes conducted primarily with astrometric or geodetic goals can be utilized for astrophysical purposes as well.


Universe ◽  
2021 ◽  
Vol 7 (6) ◽  
pp. 188
Author(s):  
Marco Berton ◽  
Emilia Järvelä

It is well known that active galactic nuclei (AGN) show various forms of interaction with their host galaxy, in a number of phenomena generally called AGN feedback. In particular, the relativistic plasma jets launched by a fraction of AGN can strongly affect their environment. We present here a study of the [O III] λλ4959,5007 lines in a diverse sample of early evolution stage AGN–specifically narrow-line Seyfert 1 galaxies. Radio imaging observations of all of the sources enable a division to jetted and non-jetted sources, and exploiting this we show that the ionized gas properties are significantly influenced by the presence of the jets, as we often find the [O III] lines (blue-)shifted with respect to their restframe wavelength. We also show how the radio morphology and the radio spectral index do not seem to play a role in the origin of the [O III] shifts, thus suggesting that the source inclination is not relevant to the lines displacement. We do not find a strong relation between the [O III] line properties and the bolometric luminosity, suggesting that within our sample radiatively driven outflows do not seem to have a significant contribution to the [O III] line kinematics. We finally suggest that [O III] shifts may be a good proxy to identify the presence of relativistic jets. Additional studies, especially with integral-field spectroscopy, will provide a deeper insight into the relation between jets and their environment in early evolution stage AGN.


1990 ◽  
Vol 115 ◽  
pp. 262-273
Author(s):  
Julian H. Krolik

AbstractHigh-resolution X-ray spectroscopy has the potential to reveal a number of interesting features of active galactic nuclei, primarily, though not exclusively, through the measurement of absorption lines. After a brief review of the principal problems of AGN research, selected potential high-resolution observations are discussed with a view toward assessing their scientific value and the degree of resolution they will require. Two classes of observations pertaining directly to AGNs are discussed: Fe Kα spectroscopy relevant to the dynamical and thermal character of the emission line zones; and measurement of resonance line absorption by highly-ionized species in BL Lac objects, which should tell us about entrainment of interstellar material by relativistic jets. A third class of potentially important observations uses AGNs as background light sources in order to directly measure the distance to clusters of galaxies.


1998 ◽  
Vol 164 ◽  
pp. 205-206
Author(s):  
Schuyler D. Van Dyk ◽  
Luis C. Ho

AbstractMany nearby galaxies show optical evidence for low-luminosity AGNs that are far less luminous than classical Seyfert nuclei and QSOs. LINERs, the most common variety of such emission-line objects, comprise ~ 1/3 of nearby galaxies, and may serve as an important “missing link“ between normal and Seyfert galaxies. To shed light on the physical origin of LINERs, which remains controversial, we are conducting a high-resolution continuum survey of a representative sample of galaxies using the VLA to search for compact radio cores. We additionally discuss the dramatic radio variability in the LINER nucleus of M81.


2020 ◽  
Vol 15 (S359) ◽  
pp. 307-311
Author(s):  
Anelise Audibert ◽  
Françoise Combes ◽  
Santiago García-Burillo ◽  
Kalliopi Dasyra

AbstractOur aim is to explore the close environment of Active Galactic Nuclei (AGN) and its connection to the host galaxy through the morphology and dynamics of the cold gas inside the central kpc in nearby AGN. We report Atacama Large Millimeter/submillimeter Array (ALMA) observations of AGN feeding and feedback caught in action in NGC613 and NGC1808 at high resolution (few pc), part of the NUclei of GAlaxies (NUGA) project. We detected trailing spirals inside the central 100 pc, efficiently driving the molecular gas into the SMBH, and molecular outflows driven by the AGN. We present preliminary results of the impact of massive winds induced by radio jets on galaxy evolution, based on observations of radio galaxies from the ALMA Radio-source Catalogue.


2001 ◽  
Vol 205 ◽  
pp. 182-189
Author(s):  
J.E. Conway

In recent years it has become possible to use high resolution radio interferometry and other techniques to study the sub-kiloparsec scale circumnuclear gas in the centres of Active Galactic Nuclei. This gas presumably provides the fuel source for the AGN activity and also plays a role in obscuring the direct view of the central engine from certain directions. The status of high resolution observations of the ionised, atomic and molecular phases of this circumnuclear gas are briefly reviewed.


1989 ◽  
Vol 134 ◽  
pp. 90-92
Author(s):  
I. C. Busko ◽  
J. E. Steiner

As part of a high resolution (0.55Å) spectroscopic survey of southern Seyfert galaxies, we observed a number of objects in the Hα region. The main goal of this survey is to study the profiles of the narrow lines in Seyfert 1 and Seyfert 2 galaxies. As a by-product, one can search for and analyse weak broad components in Ha that sometimes show up when Seyfert 2 galaxies are observed with high resolution and high signal to noise. Such objects are usually classified as Seyfert 1.8 or 1.9. The search and detailed study of these objects is of great importance for characterizing the weak end of the luminosity function of active galactic nuclei (AGN). The observations were made with a two channel intensified Reticon at the Coude spectrograph of the 1.6m telescope at the Laboratorio Nacional de Astrofisica (CNPq/LNA).


1986 ◽  
Vol 119 ◽  
pp. 573-574
Author(s):  
A S Pocock ◽  
M V Penston ◽  
M Pettini ◽  
J C Blades

The extent and physical conditions of diffuse gas in the outer regions of galaxies are currently the subject of considerable interest. A very sensitive way to probe the gas is by observing the absorption lines it produces in the spectra of background objects. However, a detailed investigation of the interstellar medium associated with external galaxies requires the availability, in the field of the galaxy under study, of several probes (QSOs, Active Galactic Nuclei, supernovae) which are: (a) sufficiently bright for high-resolution spectroscopy (B ≤ 17.5) and, (b) located over a range of projected distances from the galaxy, say from 10 to 200 kpc. As there are very few QSOs in the literature which meet these requirements, we have been carrying out a search of nearby galaxy fields for the specific purpose of finding a number of suitable background probes.


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