scholarly journals Duty cycle of the radio galaxy B2 0258+35

2018 ◽  
Vol 618 ◽  
pp. A45 ◽  
Author(s):  
M. Brienza ◽  
R. Morganti ◽  
M. Murgia ◽  
N. Vilchez ◽  
B. Adebahr ◽  
...  
Keyword(s):  
Galaxy Evolution ◽  
Duty Cycle ◽  
Spectral Properties ◽  
Surface Brightness ◽  
Large Scale ◽  
Radio Galaxy ◽  
Low Frequency ◽  
Evolutionary Stage ◽  
Low Surface Brightness ◽  
Frequency Coverage

Context. Radio loud active galactic nuclei (AGN) are episodic in nature, cycling through periods of activity and quiescence. The study of this duty cycle has recently gained new relevance because of the importance of AGN feedback for galaxy evolution. Aims. In this work we investigate the duty cycle of the radio galaxy B2 0258+35, which was previously suggested to be a restarted radio galaxy based on its morphology. The radio source consists of a pair of kpc-scale jets embedded in two large-scale lobes (∼240 kpc) with relaxed shape and very low surface brightness, which resemble remnants of a past AGN activity. Methods. We have combined new LOFAR data at 145 MHz and new Sardinia Radio Telescope data at 6600 MHz with available WSRT data at 1400 MHz to investigate the spectral properties of the outer lobes and derive their age. Results. Interestingly, the spectrum of both the outer northern and southern lobes is not ultra-steep as expected for an old ageing plasma with spectral index values equal to α1451400 = 0.48 ± 0.11 and α14006600 = 0.69 ± 0.20 in the outer northern lobe, and α1451400 = 0.73 ± 0.07 in the outer southern lobe. Moreover, despite the wide frequency coverage available for the outer northern lobe (145–6600 MHz), we do not identify a significant spectral curvature (SPC ≃ 0.2 ± 0.2). Conclusions. While mechanisms such as in-situ particle reacceleration, mixing or compression can temporarily play a role in preventing the spectrum from steepening, in no case seem the outer lobes to be compatible with being very old remnants of past activity as previously suggested (with age ≳ 80 Myr). We conclude that either the large-scale lobes are still fuelled by the nuclear engine or the jets have switched off no more than a few tens of Myr ago, allowing us to observe both the inner and outer structure simultaneously. Our study shows the importance of combining morphological and spectral properties to reliably classify the evolutionary stage of low surface brightness, diffuse emission that low frequency observations are revealing around a growing number of radio sources.

scholarly journals LOFAR view of NGC 3998, a sputtering AGN

2020 ◽  
Vol 634 ◽  
pp. A108 ◽  
Author(s):  
Sarrvesh S. Sridhar ◽  
Raffaella Morganti ◽  
Kristina Nyland ◽  
Bradley S. Frank ◽  
Jeremy Harwood ◽  
...  
Keyword(s):  
Low Power ◽  
Galaxy Evolution ◽  
Spectral Index ◽  
Surface Brightness ◽  
Large Scale ◽  
Radio Sources ◽  
The Core ◽  
Low Surface Brightness ◽  
High Turbulence ◽  
The Rich

Low-power radio sources dominate the radio sky. They tend to be small in size and dominated by their cores, but the origin of their properties and the evolution of their radio plasma are not well constrained. Interestingly, there is mounting evidence that low-power radio sources can significantly affect their surrounding gaseous medium and may therefore be more relevant for galaxy evolution than previously thought. In this paper, we present low radio frequency observations obtained with LOFAR at 147 MHz of the radio source hosted by NGC 3998. This is a rare example of a low-power source that is extremely dominated by its core, but that has two large-scale lobes of low surface brightness. We combine the new 147 MHz image with available 1400 MHz data to derive the spectral index over the source. Despite the low surface brightness, reminiscent of remnant structures, the lobes show an optically thin synchrotron spectral index (∼0.6). We interpret this as being due to rapid decollimation of the jets close to the core, to high turbulence of the plasma flow, and to entrainment of thermal gas. This could be the result of intermittent activity of the central active galactic nucleus, or, more likely, temporary disruption of the jet due to the interaction of the jet with the rich circumnuclear interstellar matter. Both would result in sputtering energy injection from the core, which would keep the lobes fed, albeit at a low rate. We discuss these results in connection with the properties of low-power radio sources in general. Our findings show that amorphous low surface brightness lobes should not be interpreted by default as remnant structures. Large deep surveys (in particular the LOFAR 150 MHz LoTSS and the recently started 1400 MHz Apertif survey) will identify a growing number of objects similar to NGC 3998 where these ideas can be further tested.

scholarly journals Linking Clustering Properties and the Evolution of Low Surface Brightness Galaxies

2007 ◽  
Vol 3 (S244) ◽  
pp. 274-278
Author(s):  
Dominik J. Bomans ◽  
S. Dominik Rosenbaum
Keyword(s):  
Galaxy Evolution ◽  
Surface Brightness ◽  
Large Scale ◽  
High Surface ◽  
Sloan Digital Sky Survey ◽  
Dark Matter Halo ◽  
Sky Survey ◽  
Low Surface Brightness ◽  
Low Surface Brightness Galaxies ◽  
Lsb Galaxies

AbstractThe reasons for the presence of two branches of galaxy evolution, one producing high surface brightness disks and one creating low surface brightness disks, is still unknown. Possible are the imprint of the properties of the dark matter halo, as well as evolutionary effects. In this paper we present an analysis of the clustering properties of LSB and HSB galaxies using the Sloan Digital Sky Survey. We show that LSB galaxies reside in regions of lower galaxy density than HSB galaxies on all scales between 0.8 and 8 Mpc, from scales of galaxy pairs to filaments of the Large Scale Structure. This implies a probable scenario of LSB galaxies preferentially forming as a result of local peaks in the large-scale valleys of the primordial density distribution.

scholarly journals Low-frequency observations of the Giant Radio Galaxy NGC 6251

2020 ◽  
Author(s):  
T M Cantwell ◽  
J D Bray ◽  
J H Croston ◽  
A M M Scaife ◽  
D D Mulcahy ◽  
...  
Keyword(s):  
Surface Brightness ◽  
Radio Galaxy ◽  
Low Frequency ◽  
External Pressure ◽  
X Ray ◽  
Upper Limit ◽  
Low Surface Brightness ◽  
Lower Limits ◽  
First Time ◽  
The Magnetic Field

Abstract We present LOFAR observations at 150 MHz of the borderline FRI/FRII giant radio galaxy NGC 6251. This paper presents the most sensitive and highest-resolution images of NGC 6251 at these frequencies to date, revealing for the first time a low-surface-brightness extension to the northern lobe, and a possible backflow associated with the southern lobe. The integrated spectra of components of NGC 6251 are consistent with previous measurements at higher frequencies, similar to results from other LOFAR studies of nearby radio galaxies. We find the outer structures of NGC 6251 to be either at equipartition or slightly electron dominated, similar to those of FRII sources rather than FRIs; but this conclusion remains tentative because of uncertainties associated with the geometry and the extrapolation of X-ray measurements to determine the external pressure distribution on the scale of the outer lobes. We place lower limits on the ages of the extension of the northern lobe and the backflow of the southern lobe of t ≳ 250 Myr and t ≳ 210 Myr respectively. We present the first detection of polarisation at 150 MHz in NGC 6251. Taking advantage of the high Faraday resolution of LOFAR, we place an upper limit on the magnetic field in the group of B < 0.2 (ΛB/10 kpc)−0.5 μG for a coherence scale of ΛB < 60 kpc and B < 13 μG for ΛB = 240 kpc.

scholarly journals The Ghosts of Galaxies: Tidal Debris in Clusters

2004 ◽  
Vol 217 ◽  
pp. 70-76
Author(s):  
Michael D. Gregg ◽  
Michael J. West
Keyword(s):  
Globular Clusters ◽  
Surface Brightness ◽  
Large Scale ◽  
Dwarf Galaxies ◽  
Cluster Formation ◽  
X Ray ◽  
Cluster Evolution ◽  
Low Surface Brightness ◽  
Intergalactic Space ◽  
Formation And Evolution

Gravitational interactions in rich clusters can strip material from the outer parts of galaxies or even completely disrupt entire systems, giving rise to large scale, low surface brightness ghostly features stretching across intergalactic space. The nearby Coma and Centaurus clusters both have striking examples of galaxy ghosts, in the form of 100 kpc-long plumes of intergalactic debris. By searching HST archival images, we have found numerous other examples of galaxy ghosts in rich clusters at low redshift, evidence that galaxy destruction and recycling are ubiquitous, important in cluster formation and evolution, and continue to mold clusters at the present epoch. Many ghosts appear in X-ray bright clusters, perhaps signaling a connection with energetic subcluster mergers.The fate of such material has important ramifications for cluster evolution. Our new HST WFPC2 V & I images of a portion of the Centaurus plume reveal that it contains an excess of discrete objects with −12 < MV < −6, consistent with being globular clusters or smaller dwarf galaxies. This tidally liberated material is being recycled directly into the intracluster population of stars, dwarf galaxies, globular clusters, and gas, which may have been built largely from a multitude of similar events over the life of the cluster.

scholarly journals The mergers in Abell 2256: displaced gas and its connection to the radio-emitting plasma

2020 ◽  
Vol 495 (4) ◽  
pp. 5014-5026 ◽  
Author(s):  
J P Breuer ◽  
N Werner ◽  
F Mernier ◽  
T Mroczkowski ◽  
A Simionescu ◽  
...  
Keyword(s):  
Surface Brightness ◽  
Large Scale ◽  
Cold Front ◽  
Low Frequency ◽  
Brightness Distribution ◽  
Analytical Models ◽  
Line Of Sight ◽  
Cluster Galaxy ◽  
X Ray ◽  
Low Entropy

ABSTRACT We present the results of deep Chandra and XMM–Newton X-ray imaging and spatially resolved spectroscopy of Abell 2256, a nearby (z = 0.058) galaxy cluster experiencing multiple mergers and displaying a rich radio morphology dominated by a large relic. The X-ray data reveal three subclusters: (i) the ‘main cluster’; (ii) the remnant of an older merger in the east of the cluster with an ∼600 kpc-long tail; (iii) a bright, bullet-like, low-entropy infalling system, with a large line-of-sight velocity component. The low-entropy system displays a 250 kpc-long cold front with a break and an intriguing surface brightness decrement. Interestingly, the infalling gas is not co-spatial with bright galaxies and the radio-loud brightest cluster galaxy of the infalling group appears dissociated from the low-entropy plasma by ∼50 kpc in projection, to the south of the eastern edge of the cold front. Assuming that the dark matter follows the galaxy distribution, we predict that it is also significantly offset from the low-entropy gas. Part of the low-frequency radio emission near the cold front might be revived by magnetic field amplification due to differential gas motions. Using analytical models and numerical simulations, we investigate the possibility that the supersonic infall of the subcluster generates a large-scale shock along our line of sight, which can be detected in the X-ray temperature map but is not associated with any clear features in the surface brightness distribution.

scholarly journals Diffuse Cluster Radio Sources

1996 ◽  
Vol 175 ◽  
pp. 333-338 ◽  
Author(s):  
L. Feretti ◽  
G. Giovannini
Keyword(s):  
Surface Brightness ◽  
Radio Galaxy ◽  
Radio Sources ◽  
Clusters Of Galaxies ◽  
Rare Phenomenon ◽  
Low Surface Brightness ◽  
Extended Sources ◽  
Formation And Evolution

Diffuse radio sources in clusters remain a poorly understood phenomenon. They are very extended sources (0.4-0.6 Mpc), of low surface brightness and steep spectrum, which cannot be identified with any active radio galaxy. They are a rare phenomenon, as they have been found so far in few clusters of galaxies. This paper reviews the current findings about this kind of sources, and the suggestions about their formation and evolution.

scholarly journals Detecting the cosmic web: Lyα emission from simulated filaments at z = 3

2020 ◽  
Vol 494 (4) ◽  
pp. 5439-5448
Author(s):  
Lydia M Elias ◽  
Shy Genel ◽  
Amiel Sternberg ◽  
Julien Devriendt ◽  
Adrianne Slyz ◽  
...  
Keyword(s):  
Surface Brightness ◽  
Large Scale ◽  
Cold Dark Matter ◽  
Image Resolution ◽  
Very Large Telescope ◽  
Filament Structure ◽  
Low Surface Brightness ◽  
Theoretical Predictions ◽  
Standard Cosmological Model ◽  
Promising Avenue

ABSTRACT The standard cosmological model (Λ cold dark matter, ΛCDM) predicts the existence of the cosmic web: a distribution of matter into sheets and filaments connecting massive haloes. However, observational evidence has been elusive due to the low surface brightness levels of the filaments. Recent deep Multi Unit Spectroscopic Explorer (MUSE)/Very Large Telescope (VLT) data and upcoming observations offer a promising avenue for Lyα detection, motivating the development of modern theoretical predictions. We use hydrodynamical cosmological simulations run with the arepo code to investigate the potential detectability of large-scale filaments, excluding contributions from the haloes embedded in them. We focus on filaments connecting massive ($M_{200c}\sim (1\!-\!3)\times 10^{12}\hbox{$\rm \, M_{\odot }$}$) haloes at z = 3, and compare different simulation resolutions, feedback levels, and mock image pixel sizes. We find increasing simulation resolution does not substantially improve detectability notwithstanding the intrinsic enhancement of internal filament structure. By contrast, for a MUSE integration of 31 h, including feedback increases the detectable area by a factor of ≃5.5 on average compared with simulations without feedback, implying that even the non-bound components of the filaments have substantial sensitivity to feedback. Degrading the image resolution from the native MUSE scale of 0.2 arcsec2 pixel−1 to 5.3 arcsec2 apertures has the strongest effect, increasing the detectable area by a median factor of ≃200 and is most effective when the size of the pixel roughly matches the width of the filament. Finally, we find the majority of Lyα emission is due to electron impact collisional excitations, as opposed to radiative recombination.

scholarly journals Radio Observations of AGN in Low Surface Brightness Galaxies

2007 ◽  
Vol 3 (S244) ◽  
pp. 352-353
Author(s):  
M. Das ◽  
S. S. McGaugh ◽  
N. Kantharia ◽  
S. N. Vogel
Keyword(s):  
Star Formation ◽  
Surface Brightness ◽  
Low Frequency ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Preliminary Results ◽  
Low Surface Brightness ◽  
Low Surface Brightness Galaxies ◽  
Lsb Galaxies ◽  
Extended Emission

AbstractWe present preliminary results of a study of the low frequency radio continuum emission from the nuclei of Giant Low Surface Brightness (LSB) galaxies. We have mapped the emission and searched for extended features such as radio lobes/jets associated with AGN activity. LSB galaxies are poor in star formation and generally less evolved compared to nearby bright spirals. This paper presents low frequency observations of 3 galaxies; PGC 045080 at 1.4 GHz, 610 MHz, 325MHz, UGC 1922 at 610 MHz and UGC 6614 at 610 MHz. The observations were done with the GMRT. Radio cores as well as extended structures were detected and mapped in all three galaxies; the extended emission may be assocated with jets/lobes associated with AGN activity. Our results indicate that although these galaxies are optically dim, their nuclei can host AGN that are bright in the radio domain.

scholarly journals Wide-Field Imaging of Halley’s Comet During 1985-1986 Using Schmidt-Type Telescopes

1984 ◽  
Vol 78 ◽  
pp. 233-235
Author(s):  
J.C. Brandt ◽  
D.A. Klinglesmith ◽  
M.B. Niedner ◽  
J. Rahe
Keyword(s):  
Time Resolution ◽  
Surface Brightness ◽  
Large Scale ◽  
Wide Field ◽  
Low Surface Brightness ◽  
The World ◽  
Halley's Comet ◽  
Worldwide Network ◽  
Field Imaging ◽  
Wide Field Imaging

AbstractPhotographic imaging of the plasma- and dust-tails of bright comets requires fast (f<4.0), wide-field (F0V>5°) optics for the proper recording of these large, low surface brightness features. Schmidts and astrographs are well-suited to this task and a large number of these instruments around the world will be turned toward Halley's Comet in 1985-1986 in support of the Large-Scale Phenomena Discipline of the International Halley Watch (IHW). This “worldwide network” should provide imagery with a time resolution never before realized in the study of a comet, and major breakthroughs in the understanding of highly-variable, elusive plasma processes in comets are expected. The imagery will also provide support for the GIOTTO, VEGA, AND PLANET-A deep space probes to the comet.

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