scholarly journals A LOFAR study of non-merging massive galaxy clusters

2019 ◽  
Vol 622 ◽  
pp. A24 ◽  
Author(s):  
F. Savini ◽  
A. Bonafede ◽  
M. Brüggen ◽  
D. Rafferty ◽  
T. Shimwell ◽  
...  
Keyword(s):  
Particle Acceleration ◽  
Radio Emission ◽  
Galaxy Clusters ◽  
Large Scale ◽  
Low Frequency ◽  
Cosmic Ray ◽  
Dynamical State ◽  
Core Cluster ◽  
Spectrum Radio ◽  
Massive Clusters

Centrally located diffuse radio emission has been observed in both merging and non-merging galaxy clusters. Depending on their morphology and size, we distinguish between giant radio haloes, which occur predominantly in merging clusters, and mini haloes, which are found in non-merging, cool-core clusters. In recent years, cluster-scale radio emission has also been observed in clusters with no sign of major mergers, showing that our knowledge of the mechanisms that lead to particle acceleration in the intra-cluster medium (ICM) is still incomplete. Low-frequency sensitive observations are required to assess whether the emission discovered in these few cases is common in galaxy clusters or not. With this aim, we carried out a campaign of observations with the LOw Frequency ARay (LOFAR) in the frequency range 120–168 MHz of nine massive clusters selected from the Planck SZ catalogue, which had no sign of major mergers. In this paper, we discuss the results of the observations that have led to the largest cluster sample studied within the LOFAR Two-metre Sky Survey, and we present Chandra X-ray data used to investigate the dynamical state of the clusters, verifying that the clusters are currently not undergoing major mergers, and to search for traces of minor or off-axis mergers. We discover large-scale steep-spectrum emission around mini haloes in the cool-core clusters PSZ1G139.61+24 and RXJ1720.1+2638, which is not observed around the mini halo in the non-cool-core cluster A1413. We also discover a new 570 kpc-halo in the non-cool-core cluster RXCJ0142.0+2131. We derived new upper limits to the radio power for clusters in which no diffuse radio emission was found, and we discuss the implication of our results to constrain the cosmic-ray energy budget in the ICM. We conclude that radio emission in non-merging massive clusters is not common at the sensitivity level reached by our observations and that no clear connection with the cluster dynamical state is observed. Our results might indicate that the sloshing of a dense cool core could trigger particle acceleration on larger scales and generate steep-spectrum radio emission.

scholarly journals A deep learning view of the census of galaxy clusters in IllustrisTNG

2020 ◽  
Vol 498 (4) ◽  
pp. 5620-5628
Author(s):  
Y Su ◽  
Y Zhang ◽  
G Liang ◽  
J A ZuHone ◽  
D J Barnes ◽  
...  
Keyword(s):  
Deep Learning ◽  
Galaxy Clusters ◽  
Large Scale ◽  
Learning Algorithm ◽  
X Ray ◽  
Deep Learning Algorithm ◽  
Cluster Evolution ◽  
Novel Method ◽  
Massive Clusters ◽  
Activation Mapping

ABSTRACT The origin of the diverse population of galaxy clusters remains an unexplained aspect of large-scale structure formation and cluster evolution. We present a novel method of using X-ray images to identify cool core (CC), weak cool core (WCC), and non-cool core (NCC) clusters of galaxies that are defined by their central cooling times. We employ a convolutional neural network, ResNet-18, which is commonly used for image analysis, to classify clusters. We produce mock Chandra X-ray observations for a sample of 318 massive clusters drawn from the IllustrisTNG simulations. The network is trained and tested with low-resolution mock Chandra images covering a central 1 Mpc square for the clusters in our sample. Without any spectral information, the deep learning algorithm is able to identify CC, WCC, and NCC clusters, achieving balanced accuracies (BAcc) of 92 per cent, 81 per cent, and 83 per cent, respectively. The performance is superior to classification by conventional methods using central gas densities, with an average ${\rm BAcc}=81{{\ \rm per\ cent}}$, or surface brightness concentrations, giving ${\rm BAcc}=73{{\ \rm per\ cent}}$. We use class activation mapping to localize discriminative regions for the classification decision. From this analysis, we observe that the network has utilized regions from cluster centres out to r ≈ 300 kpc and r ≈ 500 kpc to identify CC and NCC clusters, respectively. It may have recognized features in the intracluster medium that are associated with AGN feedback and disruptive major mergers.

scholarly journals The spectacular cluster chain Abell 781 as observed with LOFAR, GMRT, and XMM-Newton

2019 ◽  
Vol 622 ◽  
pp. A19 ◽  
Author(s):  
A. Botteon ◽  
T. W. Shimwell ◽  
A. Bonafede ◽  
D. Dallacasa ◽  
F. Gastaldello ◽  
...  
Keyword(s):  
Radio Emission ◽  
Large Scale ◽  
Thermal Emission ◽  
Low Frequency ◽  
Current Data ◽  
Mass Relation ◽  
Radio Halo ◽  
Main Cluster ◽  
Upper Limit ◽  
Main Component

Context. A number of merging galaxy clusters show the presence of large-scale radio emission associated with the intra-cluster medium (ICM). These synchrotron sources are generally classified as radio haloes and radio relics. Aims. Whilst it is commonly accepted that mergers play a crucial role in the formation of radio haloes and relics, not all the merging clusters show the presence of giant diffuse radio sources and this provides important information concerning current models. The Abell 781 complex is a spectacular system composed of an apparent chain of clusters on the sky. Its main component is undergoing a merger and hosts peripheral emission that is classified as a candidate radio relic and a disputed radio halo. Methods. We used new LOw Frequency ARay (LOFAR) observations at 143 MHz and archival Giant Metrewave Radio Telescope (GMRT) observations at 325 and 610 MHz to study radio emission from non-thermal components in the ICM of Abell 781. Complementary information came from XMM-Newton data, which allowed us to investigate the connection with the thermal emission and its complex morphology. Results. The origin of the peripheral emission is still uncertain. We speculate that it is related to the interaction between a head tail radio galaxy and shock. However, the current data allow us only to set an upper limit of ℳ <  1.4 on the Mach number of this putative shock. Instead, we successfully characterise the surface brightness and temperature jumps of a shock and two cold fronts in the main cluster component of Abell 781. Their positions suggest that the merger is involving three substructures. We do not find any evidence for a radio halo either at the centre of this system or in the other clusters of the chain. We place an upper limit to the diffuse radio emission in the main cluster of Abell 781 that is a factor of 2 below the current radio power-mass relation for giant radio haloes.

scholarly journals A giant radio bridge connecting two clusters in Abell 1758

2020 ◽  
Author(s):  
A Botteon ◽  
R J van Weeren ◽  
G Brunetti ◽  
F de Gasperin ◽  
H T Intema ◽  
...  
Keyword(s):  
Radio Emission ◽  
Galaxy Clusters ◽  
Large Scale ◽  
Synchrotron Emission ◽  
X Ray ◽  
Compressed Gas ◽  
Order Of Magnitude ◽  
Thermal Phenomena ◽  
Cluster Pair ◽  
Radio Halos

Abstract Collisions between galaxy clusters dissipate enormous amounts of energy in the intra-cluster medium (ICM) through turbulence and shocks. In the process, Mpc-scale diffuse synchrotron emission in form of radio halos and relics can form. However, little is known about the very early phase of the collision. We used deep radio observations from 53 MHz to 1.5 GHz to study the pre-merging galaxy clusters A1758N and A1758S that are ∼2 Mpc apart. We confirm the presence of a giant bridge of radio emission connecting the two systems that was reported only tentatively in our earlier work. This is the second large-scale radio bridge observed to date in a cluster pair. The bridge is clearly visible in the LOFAR image at 144 MHz and tentatively detected at 53 MHz. Its mean radio emissivity is more than one order of magnitude lower than that of the radio halos in A1758N and A1758S. Interestingly, the radio and X-ray emissions of the bridge are correlated. Our results indicate that non-thermal phenomena in the ICM can be generated also in the region of compressed gas in-between infalling systems.

scholarly journals Murchison Widefield Array detection of steep-spectrum, diffuse, non-thermal radio emission within Abell 1127

2020 ◽  
Vol 37 ◽  
Author(s):  
S. W. Duchesne ◽  
M. Johnston-Hollitt ◽  
Z. Zhu ◽  
R. B. Wayth ◽  
J. L. B. Line
Keyword(s):  
Radio Emission ◽  
Galaxy Clusters ◽  
Phase Ii ◽  
Thermal Emission ◽  
Low Frequency ◽  
Radio Spectrum ◽  
Discrete Source ◽  
Thermal Radio ◽  
Thermal Radio Emission ◽  
Murchison Widefield Array

Abstract Diffuse, non-thermal emission in galaxy clusters is increasingly being detected in low-frequency radio surveys and images. We present a new diffuse, steep-spectrum, non-thermal radio source within the cluster Abell 1127 found in survey data from the Murchison Widefield Array (MWA). We perform follow-up observations with the ‘extended’ configuration MWA Phase II with improved resolution to better resolve the source and measure its low-frequency spectral properties. We use archival Very Large Array S-band data to remove the discrete source contribution from the MWA data, and from a power law model fit we find a spectral index of –1.83±0.29 broadly consistent with relic-type sources. The source is revealed by the Giant Metrewave Radio Telescope at 150 MHz to have an elongated morphology, with a projected linear size of 850 kpc as measured in the MWA data. Using Chandra observations, we derive morphological estimators and confirm quantitatively that the cluster is in a disturbed dynamical state, consistent with the majority of phoenices and relics being hosted by merging clusters. We discuss the implications of relying on morphology and low-resolution imaging alone for the classification of such sources and highlight the usefulness of the MHz to GHz radio spectrum in classifying these types of emission. Finally, we discuss the benefits and limitations of using the MWA Phase II in conjunction with other instruments for detailed studies of diffuse, steep-spectrum, non-thermal radio emission within galaxy clusters.

COSMOLOGICAL SHOCK WAVES IN THE LARGE SCALE STRUCTURE OF THE UNIVERSE

2013 ◽  
Vol 23 ◽  
pp. 386-390
Author(s):  
RENYI MA ◽  
DONGSU RYU ◽  
HYESUNG KANG
Keyword(s):  
Shock Waves ◽  
Galaxy Clusters ◽  
Large Scale ◽  
Gamma Ray ◽  
High Redshift ◽  
Cosmic Ray ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Weak Shocks ◽  
The Universe

Based on the cosmological hydrodynamic simulation, we study the properties of shock waves formed during the formation of the large scale structure (LSS) of the universe, and investigate their contribution to the cosmic ray (CR) fraction in the intergalactic medium (IGM). It is found that while strong accretion shocks prevail at high redshift, weak internal shocks become dominant in the intracluster medium (ICM) as galaxy clusters form and virialize at low redshift, z < 1. The accumulated CR proton energy is likely to be less than 10 % of the thermal energy in the ICM, since weak shocks of M ≲ 3 are most abundant. This is consistent with the upper limit constrained by radio and gamma-ray observations of galaxy clusters. In the warm-hot medium (WHIM) inside filaments, CRs and gas could be almost in energy equipartition, since relatively stronger shocks of 5 ≲ M ≲ 10 are dominant there. We suggest that the non-thermal emissions from the CR electrons and protons accelerated by cosmological shock waves could provide a new way to detect the WHIM of the universe.

scholarly journals CHANG-ES XII

2019 ◽  
Vol 622 ◽  
pp. A9 ◽  
Author(s):  
A. Miskolczi ◽  
V. Heesen ◽  
C. Horellou ◽  
D.-J. Bomans ◽  
R. Beck ◽  
...  
Keyword(s):  
Spectral Index ◽  
Large Scale ◽  
Low Frequency ◽  
Cosmic Ray ◽  
Radio Continuum ◽  
Dark Matter Halo ◽  
Very Large Array ◽  
Star Forming ◽  
Pure Diffusion ◽  
The Galaxy

Context. Low-frequency radio continuum studies of star-forming edge-on galaxies can help to further understand how cosmic-ray electrons (CRe) propagate through the interstellar medium into the halo and how this is affected by energy losses and magnetic fields. Aims. Observations with the Very Large Array (VLA) from Continuum Haloes in Nearby Galaxies – an EVLA Survey (CHANG-ES) are combined with those with the LOw Frequency ARray (LOFAR) from the LOFAR Two-metre Sky Survey (LoTSS ) to identify the prevailing mode of cosmic-ray transport in the edge-on spiral galaxy NGC 3556. Methods. We mapped the radio spectral index, magnetic field strength, and orientation using VLA 1.5 and 6 GHz and LOFAR 144 MHz data, and we fit 1D cosmic-ray propagation models to these maps using SPINNAKER (Spectral Index Numerical Analysis of K(c)osmic-ray electron radio emission) and its interactive wrapper SPINTERACTIVE. Results. We find that the spectral index in the galactic midplane is, as expected for young CRe, α ≈ −0.7 and steepens towards the halo of the galaxy as a consequence of spectral ageing. The intensity scale heights are about 1.4 and 1.9 kpc for the thin disc, and 3.3 and 5.9 kpc for the thick disc at 1.5 GHz and 144 MHz, respectively. While pure diffusion cannot explain our data, advection can, particularly if we assume a linearly accelerating wind. Our best-fitting model has an initial speed of 123 km s−1 in the galactic midplane and reaches the escape velocity at heights between 5 kpc and 15 kpc above the disc, depending on the assumed dark matter halo of the galaxy. This galactic wind scenario is corroborated by the existence of vertical filaments seen both in the radio continuum and in H α in the disc-halo interface and of a large-scale reservoir of hot, X-ray emitting gas in the halo. Conclusions. Radio haloes show the existence of galactic winds, possibly driven by cosmic rays, in typical star-forming spiral galaxies.

scholarly journals Diffuse radio emission in the galaxy cluster SPT-CL J2031−4037: a steep-spectrum intermediate radio halo?

2020 ◽  
Vol 493 (1) ◽  
pp. L28-L32 ◽  
Author(s):  
Ramij Raja ◽  
Majidul Rahaman ◽  
Abhirup Datta ◽  
Jack O Burns ◽  
H T Intema ◽  
...  
Keyword(s):  
Radio Emission ◽  
Spectral Index ◽  
Low Frequency ◽  
Galaxy Cluster ◽  
Transition System ◽  
Cluster Galaxy ◽  
Radio Halo ◽  
Spectrum Radio ◽  
Upper Limits ◽  
The Galaxy

ABSTRACT The advent of sensitive low-frequency radio observations has revealed a number of diffuse radio objects with peculiar properties that are challenging our understanding of the physics of the intracluster medium. Here, we report the discovery of a steep-spectrum radio halo surrounding the central brightest cluster galaxy (BCG) in the galaxy cluster SPT-CL J2031−4037. This cluster is morphologically disturbed yet has a weak cool core, an example of a cool-core/non-cool-core transition system, which harbours a radio halo ∼0.7 Mpc in size. The halo emission detected at 1.7 GHz is less extended compared to that in the 325 MHz observation, and the spectral index of the part of the halo visible at the 325 MHz to 1.7 GHz frequencies was found to be −1.35 ± 0.07. Also, P1.4 GHz was found to be 0.77 × 1024 W Hz−1, which falls in the region where radio mini-haloes, halo upper limits and ultra-steep-spectrum (USS) haloes are found in the P1.4 GHz–LX plane. Additionally, simulations presented in the paper provide support for the scenario of the steep spectrum. The diffuse radio emission found in this cluster may be a steep-spectrum ‘intermediate’ or ‘hybrid’ radio halo that is transitioning into a mini-halo.

scholarly journals Models of particle acceleration in galaxy clusters by MHD turbulence

2009 ◽  
Vol 5 (H15) ◽  
pp. 466-467
Author(s):  
G. Brunetti
Keyword(s):  
Particle Acceleration ◽  
Radio Emission ◽  
Galaxy Clusters ◽  
Indirect Evidence ◽  
Mhd Turbulence ◽  
Radio Data ◽  
Central Cluster ◽  
Relativistic Particles

AbstractPresent radio data provide indirect evidence that diffuse radio emission in the central cluster regions may originate from turbulent-acceleration of relativistic particles. I was invited to discuss models of particle acceleration by MHD turbulence in clusters and in these pages I briefly touch the main points of my talk.

scholarly journals Limiting the shock acceleration of cosmic ray protons in the ICM

2020 ◽  
Vol 495 (1) ◽  
pp. L112-L117 ◽  
Author(s):  
D Wittor ◽  
F Vazza ◽  
D Ryu ◽  
H Kang
Keyword(s):  
Cosmic Rays ◽  
Galaxy Clusters ◽  
Large Scale ◽  
Cosmic Ray ◽  
Shock Acceleration ◽  
Diffusive Shock Acceleration ◽  
Magnetic Field Topology ◽  
Tracer Particles ◽  
Γ Rays ◽  
Massive Galaxy

ABSTRACT Observations of large-scale radio emissions prove the existence of shock accelerated cosmic ray electrons in galaxy clusters, while the lack of detected γ-rays limits the acceleration of cosmic ray protons in galaxy clusters. This challenges our understanding of how diffusive shock acceleration works. In this work, we couple the most updated recipes for shock acceleration in the intracluster medium to state-of-the-art magnetohydrodynamical simulations of massive galaxy clusters. Furthermore, we use passive tracer particles to follow the evolution of accelerated cosmic rays. We show that when the interplay between magnetic field topology and the feedback from accelerated cosmic rays is taken into account, the latest developments of particle acceleration theory give results that are compatible with observational constraints.

scholarly journals Particle Acceleration Mechanisms

1994 ◽  
Vol 142 ◽  
pp. 515-520
Author(s):  
R. D. Blandford
Keyword(s):  
Particle Acceleration ◽  
Large Scale ◽  
Magnetic Energy ◽  
Cosmic Ray ◽  
High Energy ◽  
High Energy Particle ◽  
Common Channel ◽  
Energy Particle ◽  
Particle Injection ◽  
Physical Mechanisms

AbstractHigh-energy particle acceleration is observed to proceed in a diverse variety of astrophysical sites ranging from the terrestrial aurorae to the most distant quasars. Particle acceleration is a fairly common channel for the release of large-scale kinetic, rotational, and magnetic energy. Physical mechanisms include electrostatic acceleration, stochastic processes and diffusive shock energization. Cosmic-ray energy spectra have shapes which reflect escape, collisional, and radiative losses. The overall acceleration efficiency is controlled by the low-energy particle injection which may, in turn, feed back into the energization. Recent observational developments, which illustrate these general principles and raise fresh questions, are briefly summarized.Subject heading: acceleration of particles

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