scholarly journals Optical Nuclear Activity in Radio Galaxies in Clusters

1989 ◽  
Vol 134 ◽  
pp. 457-459
Author(s):  
H. K. C. Yee ◽  
M. M. De Robertis
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Radio Galaxies ◽  
Elliptical Galaxies ◽  
Substantial Fraction ◽  
Strong Emission ◽  
Nuclear Activity ◽  
Time Period ◽  
Class 1 ◽  
Short Time

It has traditionally been accepted that quasars and strong emission-line radio galaxies, although situated in regions of enhanced galaxy density, are rarely found within rich clusters (Yee and Green 1984; Longair and Seldner 1978). The recent finding by Yee and Green (1987) that at z ≳0.5 a substantial fraction of optically bright radio-loud quasars are found in galaxy clusters as rich as Abell class 1, suggests that a substantial evolution of the environments of rich clusters has taken place over this short time period. Similar results for radio galaxies have also been obtained by Hill and Lilly (1988, private communication). If this is an evolutionary effect, then at least some first-rank elliptical galaxies in low-redshift rich clusters must contain remnants of active galactic nuclei (AGN). Motivated by this, we attempted to find traces of AGN-like activity in a sample of FR class I radio galaxies which are known to be “quiescent” absorption-line systems situated in low-redshift clusters.

scholarly journals Optical Spectra of Radio-Loud and Radio-Quiet Active Galactic Nuclei

1982 ◽  
Vol 97 ◽  
pp. 369-371 ◽  
Author(s):  
Donald E. Osterbrock
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Radio Galaxies ◽  
Optical Spectra ◽  
Emission Lines ◽  
Radio Sources ◽  
Strong Emission ◽  
Normal Galaxies ◽  
Many Sources

Many radio galaxies have strong emission lines in their optical spectra. The fraction with such lines is much larger than in “normal” galaxies. Radio galaxies generally also have very bright nuclei; thus those with strong emission lines are similar in both respects to Seyfert galaxies. Hence radio and Seyfert galaxies are both generally considered to be similar physical objects: active galactic nuclei. Their observational properties show they are closely related to quasars (quasi-stellar radio sources) and (radio-quiet) QSOs. A short table of the space density of these objects, culled from many sources, chiefly Schmidt (1978) and Simkim, Su and Schwarz (1980) is given below. Although all the numbers are quite uncertain, there is no doubt that the radio-loud objects are relatively rare. With less certainty, it appears that the ratio of numbers of radio galaxies to Seyfert galaxies is about the same as the ratio of numbers of quasars to QSOs.

The co-responsibility of mass and environment in the formation of lenticular galaxies

2020 ◽  
Vol 15 (S359) ◽  
pp. 173-174
Author(s):  
A. Cortesi ◽  
L. Coccato ◽  
M. L. Buzzo ◽  
K. Menéndez-Delmestre ◽  
T. Goncalves ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Maximum Likelihood Method ◽  
Spiral Galaxies ◽  
Galactic Nuclei ◽  
Rotation Velocity ◽  
Elliptical Galaxies ◽  
Likelihood Method ◽  
Data Set ◽  
Lenticular Galaxies ◽  
Galaxies Kinematics

AbstractWe present the latest data release of the Planetary Nebulae Spectrograph Survey (PNS) of ten lenticular galaxies and two spiral galaxies. With this data set we are able to recover the galaxies’ kinematics out to several effective radii. We use a maximum likelihood method to decompose the disk and spheroid kinematics and we compare it with the kinematics of spiral and elliptical galaxies. We build the Tully- Fisher (TF) relation for these galaxies and we compare with data from the literature and simulations. We find that the disks of lenticular galaxies are hotter than the disks of spiral galaxies at low redshifts, but still dominated by rotation velocity. The mechanism responsible for the formation of these lenticular galaxies is neither major mergers, nor a gentle quenching driven by stripping or Active Galactic Nuclei (AGN) feedback.

scholarly journals Excitation mechanism in the intracluster filaments surrounding the Brightest Cluster Galaxies

2019 ◽  
Vol 15 (S359) ◽  
pp. 185-187
Author(s):  
Fiorella L. Polles
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Elliptical Galaxies ◽  
Cluster Galaxies ◽  
Cooling Flow ◽  
Submillimeter Wavelengths ◽  
Hot Plasma ◽  
Brightest Cluster Galaxies ◽  
Multi Phase ◽  
The Impact

AbstractMulti-phase filamentary structures surrounding giant elliptical galaxies at the center of cool-core clusters, the Brightest Cluster Galaxies (BCGs), have been detected from optical to submillimeter wavelengths. The source of the ionisation in the filaments is still debated. Studying the excitation of these structures is key to our understanding of Active Galactic Nuclei (AGN) feedback in general, and more precisely of the impact of environmental and local effects on star formation. One possible contributor to the excitation of the filaments is the thermal radiation from the cooling of the hot plasma surrounding the BCGs, the so-called cooling flow.

scholarly journals Luminosity Correlation of the X-ray Selected Radio-Loud AGNs

1999 ◽  
Vol 194 ◽  
pp. 306-310
Author(s):  
Q. Yuan ◽  
J. Wu ◽  
K. Huang
Keyword(s):  
Active Galactic Nuclei ◽  
Broad Band ◽  
Galactic Nuclei ◽  
Radio Galaxies ◽  
Spectral Indices ◽  
Strong Correlations ◽  
Band Energy ◽  
X Ray ◽  
Sky Survey ◽  
Bl Lacs

This paper presents a test of the luminosity correlation of the X-ray selected radio-loud Active Galactic Nuclei (AGNs), based on a large sample constructed by combining our cross-identification of southern sky sources with the radio-loud sources in the northern hemisphere given by Brinkmann et al. (1995). All sources were detected both by the ROSAT All-Sky Survey and the radio surveys at 4.85 GHz. The broad band energy distribution confirms the presence of strong correlations between luminosities in the radio, optical, and X-ray bands which differ for quasars, seyferts, BL Lacs, and radio galaxies. The tight correlations between spectral indices αox and monochromatic luminosities at 5500 Å and 4.85 GHz are also shown.

scholarly journals The Milliarcsecond Structure of Active Galactic Nuclei Observed with VLBI

1989 ◽  
Vol 134 ◽  
pp. 525-528
Author(s):  
T. J. Pearson ◽  
A. C. S. Readhead
Keyword(s):  
Active Galactic Nuclei ◽  
Very Long Baseline Interferometry ◽  
Galactic Nuclei ◽  
Radio Galaxies ◽  
Relativistic Motion ◽  
Powerful Radio ◽  
Long Baseline ◽  
Vlbi Observations ◽  
Central Engine

Very Long Baseline Interferometry at radio wavelengths is the only technique available for imaging the central few parsecs of powerful radio galaxies and quasars. VLBI observations have shown that in many nuclei radio-emitting material is collimated into a jet on a scale less than a parsec and ejected at relativistic velocities. The interpretation of the observations is complicated by the relativistic motion, however: the images are dominated by those parts of the source that are moving almost directly towards the observer, and thus amplified by relativistic aberration. Nonetheless, the VLBI images are vital for understanding the nature of the central engine, the cause of the collimation, and the physics of the jets.

scholarly journals Collimated Bipolar Outflow and the Formation of Nuclear Spirals; Possible Role of Magnetic Fields

1990 ◽  
Vol 140 ◽  
pp. 447-448
Author(s):  
P. Pismis ◽  
E. Moreno ◽  
A. Garcia-Barreto
Keyword(s):  
Magnetic Fields ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Radio Galaxies ◽  
The Past ◽  
Bipolar Outflow ◽  
The Difference ◽  
Observational Techniques ◽  
Quasars And Radio Galaxies

The existence of non–steady phenomena, namely activity in the form of radial motions (outflow) of matter from the nuclei of galaxies is well established at present. Active Galactic Nuclei (AGN) constitute a topic of great interest and are intensively studied by all existing observational techniques. Conventionally objects classified as AGN span a range from quasars, radio galaxies to Seyferts 1 and 2. It appears, however, that there exist galaxies which exhibit somewhat milder activity which does not qualify their inclusion in the AGN group. The designation of MAGN (M for mildly) was suggested in the past (Pismis, 1986) to cover the less energetic nuclei. It may be reasonable to consider that active nuclei form a sequence, the difference along it being due to the energetics of the nuclei, from the most active quasars and radio galaxies down to the mildest ones like M31 or our Galaxy. The phenomenon underlying the activity may thus be universal, subject to the intrinsic energetics of the nuclei (Pismis, 1987).

scholarly journals Short Time Scale Variability of Active Galactic Nuclei: Einstein IPC Observations of PKS 2155-304 - A Report of Rapid Variations of Instrumental Origin

1989 ◽  
Vol 134 ◽  
pp. 106-107
Author(s):  
J. H. Beall ◽  
W. A. Snyder ◽  
K. S. Wood
Keyword(s):  
Active Galactic Nuclei ◽  
Time Scales ◽  
Time Scale ◽  
Galactic Nuclei ◽  
Short Time Scale ◽  
Background Region ◽  
Rapid Changes ◽  
Source Models ◽  
The Mean ◽  
Short Time

The Einstein IPC observed the bright (5 mCrab) X-ray emitting BL Lac Object PKS 2155-304 on 1979 November 4th and 5th through 7th and on 1980 May 16th through 18th. A total of 17.4 hours were spent monitoring the source. Changes in intensity of between 10–50% are evident in the data for time scales of days and months. The source was constant to within 10% of the mean intensity on hourly time scales for all intervals of data except one. Repeated factor of 2 variations in intensity, occuring on 10–30 second time scales, were observed during the first 50 minutes of the 1979 Nov. 5th observation. These variations, however, were anticorrelated with variations seen in an adjacent background region. Concurrent MPC observations also failed to confirm the rapid changes, although they should have been readily detected. Thus, we conclude that the observed rapid variations are not intrinsic to the source, but originated in the IPC. These results can have implications for other IPC reports of short time scale variability for active galaxies and for source models based on such observations.

scholarly journals Combining LOFAR and Apertif Data for Understanding the Life Cycle of Radio Galaxies

Galaxies ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 88
Author(s):  
Raffaella Morganti ◽  
Nika Jurlin ◽  
Tom Oosterloo ◽  
Marisa Brienza ◽  
Emanuela Orrú ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Phased Array ◽  
Low Frequency ◽  
Galactic Nuclei ◽  
Radio Galaxies ◽  
Host Galaxy ◽  
Evolutionary Stage ◽  
Spectral Indices ◽  
Feed System ◽  
Lockman Hole

Active galactic nuclei (AGN) at the centres of galaxies can cycle between periods of activity and of quiescence. Characterising the duty-cycle of AGN is crucial for understanding their impact on the evolution of the host galaxy. For radio AGN, their evolutionary stage can be identified from a combination of morphological and spectral properties. We summarise the results we have obtained in the last few years by studying radio galaxies in various crucial phases of their lives, such as remnant and restarted sources. We used morphological information derived from LOw Frequency ARray (LOFAR) images at 150 MHz, combined with resolved spectral indices maps, obtained using recently released images at 1400 MHz from the APERture Tile In Focus (Apertif) phased-array feed system installed on the Westerbork Synthesis Radio Telescope. Our study, limited so far to the Lockman Hole region, has identified radio galaxies in the dying and restarted phases. We found large varieties in their properties, relevant for understanding their evolutionary stage. We started by quantifying their occurrences, the duration of the ‘on’ (active) and ‘off’ (dying) phase, and we compared the results with models of the evolution of radio galaxies. In addition to these extreme phases, the resolved spectral index images can also reveal interesting secrets about the evolution of apparently normal radio galaxies. The spectral information can be connected with, and used to improve, the Fanaroff–Riley classification, and we present one example of this, illustrating what the combination of the LOFAR and Apertif surveys now allow us to do routinely.

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