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 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 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.

ASIC Implementation of a Nonlinear Dynamical Model for Hippocampal Prosthesis

2018 ◽  
Vol 30 (9) ◽  
pp. 2472-2499 ◽  
Author(s):  
Zhitong Qiao ◽  
Yan Han ◽  
Xiaoxia Han ◽  
Han Xu ◽  
Will X. Y. Li ◽  
...  
Keyword(s):  
Low Power ◽  
Integrated Circuit ◽  
Large Scale ◽  
Random Number Generator ◽  
Core Area ◽  
Dynamical Model ◽  
Volterra Model ◽  
Nonlinear Dynamical ◽  
The Core ◽  
Nonlinear Dynamical Model

A hippocampal prosthesis is a very large scale integration (VLSI) biochip that needs to be implanted in the biological brain to solve a cognitive dysfunction. In this letter, we propose a novel low-complexity, small-area, and low-power programmable hippocampal neural network application-specific integrated circuit (ASIC) for a hippocampal prosthesis. It is based on the nonlinear dynamical model of the hippocampus: namely multi-input, multi-output (MIMO)–generalized Laguerre-Volterra model (GLVM). It can realize the real-time prediction of hippocampal neural activity. New hardware architecture, a storage space configuration scheme, low-power convolution, and gaussian random number generator modules are proposed. The ASIC is fabricated in 40 nm technology with a core area of 0.122 mm[Formula: see text] and test power of 84.4 [Formula: see text]W. Compared with the design based on the traditional architecture, experimental results show that the core area of the chip is reduced by 84.94% and the core power is reduced by 24.30%.

scholarly journals The VISCACHA survey – II. Structure of star clusters in the Magellanic Clouds periphery

2020 ◽  
Vol 498 (1) ◽  
pp. 205-222
Author(s):  
João F C Santos ◽  
Francisco F S Maia ◽  
Bruno Dias ◽  
Leandro de O Kerber ◽  
Andrés E Piatti ◽  
...  
Keyword(s):  
Surface Brightness ◽  
Structural Parameters ◽  
Star Clusters ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
The Core ◽  
Optical Images ◽  
Low Surface Brightness ◽  
Homogeneous Set ◽  
Stellar Density

ABSTRACT We provide a homogeneous set of structural parameters of 83 star clusters located at the periphery of the Small Magellanic Cloud (SMC) and the Large Magellanic Cloud (LMC). The clusters’ stellar density and surface brightness profiles were built from deep, AO assisted optical images, and uniform analysis techniques. The structural parameters were obtained from King and Elson et al. model fittings. Integrated magnitudes and masses (for a subsample) are also provided. The sample contains mostly low surface brightness clusters with distances between 4.5 and 6.5 kpc and between 1 and 6.5 kpc from the LMC and SMC centres, respectively. We analysed their spatial distribution and structural properties, comparing them with those of inner clusters. Half-light and Jacobi radii were estimated, allowing an evaluation of the Roche volume tidal filling. We found that: (i) for our sample of LMC clusters, the tidal radii are, on average, larger than those of inner clusters from previous studies; (ii) the core radii dispersion tends to be greater for LMC clusters located towards the southwest, with position angles of ∼200° and about ∼5° from the LMC centre, i.e. those LMC clusters nearer to the SMC; (iii) the core radius evolution for clusters with known age is similar to that of inner clusters; (iv) SMC clusters with galactocentric distances closer than 4 kpc are overfilling; (v) the recent Clouds collision did not leave marks on the LMC clusters’ structure that our analysis could reveal.

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 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 Large Scale Jets in Class I and Class II Radio Sources and Quasars

1989 ◽  
Vol 8 ◽  
pp. 409-416
Author(s):  
G.V. Bicknell
Keyword(s):  
Interstellar Medium ◽  
Surface Brightness ◽  
Large Scale ◽  
External Medium ◽  
Class Ii ◽  
Class I ◽  
Radio Sources ◽  
Speed Of Light ◽  
Slow Surface ◽  
Quasar Jets

ABSTRACTThe physics of large scale jets in class I and class II extragalactic radio sources and quasars is discussed. Class I jets appear to be turbulent, transonic jets which entrain the interstellar medium. The related jet deceleration causes a slow surface brightness decline which is usually observed. Class II jets are supersonic and terminate in an advancing shock against the external medium. Both types of jet are initially light but the ratio of jet density to external density of class I jets increases owing to entrainment. It is quite plausible that quasar jets are hypersonic and light and this may solve problems of confinement. The velocities of class I jets are of the order of a few thousand kilometers per second. Class II and quasar jets may be at least mildly relativistic. However, it is not clear whether the velocities of large scale jets in powerful sources are close to the speed of light. Recent depolarization measurements provide an interesting focus for discussion of this question.

scholarly journals Probing Galactic Outskirts with Dragonfly

2016 ◽  
Vol 11 (S321) ◽  
pp. 137-146 ◽  
Author(s):  
Roberto Abraham ◽  
Allison Merritt ◽  
Jielai Zhang ◽  
Pieter van Dokkum ◽  
Charlie Conroy ◽  
...  
Keyword(s):  
Surface Brightness ◽  
Wide Field ◽  
Rich Variety ◽  
Neutral Gas ◽  
Early Results ◽  
Low Surface Brightness ◽  
Stellar Halo ◽  
Nearby Galaxies ◽  
The Mean ◽  
The Rich

AbstractWe describe the challenges inherent to low surface brightness imaging and present some early results from the Dragonfly Nearby Galaxies survey. Wide field, ultra-low surface brightness imaging (μg > 31 mag arcsec−2) of the first eight galaxies in the survey reveals a rich variety in the distribution of stars in the outskirts of luminous nearby galaxies. The mean stellar halo mass fraction is 0.009 ± 0.005 with a peak-to-peak scatter of a factor of > 100. Some galaxies in the sample feature strongly structured halos resembling that of M31, but three of the eight galaxies have halos that are completely undetected in our data. We conclude that spiral galaxies as a class exhibit a rich variety in stellar halo properties, implying that their assembly histories have been highly non-uniform. While the outskirts of some galaxies are dominated by halos with the rich substructures predicted by numerical simulations, in other cases the outermost parts of galaxies are simply the extrapolated smooth starlight from enormous stellar disks that closely trace neutral gas morphology out to around 20 scale lengths.

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.

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