We review the present theoretical and numerical understanding of magnetic field amplification in cosmic large-scale structure, on length scales of galaxy clusters and beyond. Structure formation ...drives compression and turbulence, which amplify tiny magnetic seed fields to the microGauss values that are observed in the intracluster medium. This process is intimately connected to the properties of turbulence and the microphysics of the intra-cluster medium. Additional roles are played by merger induced shocks that sweep through the intra-cluster medium and motions induced by sloshing cool cores. The accurate simulation of magnetic field amplification in clusters still poses a serious challenge for simulations of cosmological structure formation. We review the current literature on cosmological simulations that include magnetic fields and outline theoretical as well as numerical challenges.
ABSTRACT
Radio relics are vast synchrotron sources that sit on the outskirts of merging galaxy clusters. In this work we model their formation using a Press–Schechter formalism to simulate merger ...rates, analytical models for the intracluster medium and the shock dynamics, as well as a simple model for the cosmic ray electrons at the merger shocks. We show that the statistical properties of the population of radio relics are strongly dependent on key physical parameters, such as the acceleration efficiency, the magnetic field strength at the relic, the geometry of the relic and the duration of the electron acceleration at merger shocks. It turns out that the flux distribution as well as the power–mass relation can constrain key parameters of the intracluster medium. With the advent of new large-area radio surveys, statistical analyses of radio relics will complement what we have learned from observations of individual objects.
In a growing number of galaxy clusters diffuse extended radio sources have been found. These sources are not directly associated with individual cluster galaxies. The radio emission reveal the ...presence of cosmic rays and magnetic fields in the intracluster medium (ICM). We classify diffuse cluster radio sources into radio halos, cluster radio shocks (relics), and revived AGN fossil plasma sources. Radio halo sources can be further divided into giant halos, mini-halos, and possible “intermediate” sources. Halos are generally positioned at cluster center and their brightness approximately follows the distribution of the thermal ICM. Cluster radio shocks (relics) are polarized sources mostly found in the cluster’s periphery. They trace merger induced shock waves. Revived fossil plasma sources are characterized by their radio steep-spectra and often irregular morphologies. In this review we give an overview of the properties of diffuse cluster radio sources, with an emphasis on recent observational results. We discuss the resulting implications for the underlying physical acceleration processes that operate in the ICM, the role of relativistic fossil plasma, and the properties of ICM shocks and magnetic fields. We also compile an updated list of diffuse cluster radio sources which will be available on-line (
http://galaxyclusters.com
). We end this review with a discussion on the detection of diffuse radio emission from the cosmic web.
The amplification of primordial magnetic fields via a small-scale turbulent dynamo during structure formation might be able to explain the observed magnetic fields in galaxy clusters. The ...magnetization of more tenuous large-scale structures such as cosmic filaments is more uncertain, as it is challenging for numerical simulations to achieve the required dynamical range. In this work, we present magnetohydrodynamical cosmological simulations on large uniform grids to study the amplification of primordial seed fields in the intracluster medium (ICM) and in the warm–hot-intergalactic medium (WHIM). In the ICM, we confirm that turbulence caused by structure formation can produce a significant dynamo amplification, even if the amplification is smaller than what is reported in other papers. In the WHIM inside filaments, we do not observe significant dynamo amplification, even though we achieve Reynolds numbers of R
e ∼ 200–300. The maximal amplification for large filaments is of the order of ∼100 for the magnetic energy, corresponding to a typical field of a few ∼nG starting from a primordial weak field of 10−10 G (comoving). In order to start a small-scale dynamo, we found that a minimum of ∼102 resolution elements across the virial radius of galaxy clusters was necessary. In filaments we could not find a minimum resolution to set off a dynamo. This stems from the inefficiency of supersonic motions in the WHIM in triggering solenoidal modes and small-scale twisting of magnetic field structures. Magnetic fields this small will make it hard to detect filaments in radio observations.
The eROSITA X-ray telescope on SRG Predehl, P.; Andritschke, R.; Arefiev, V. ...
Astronomy & astrophysics,
03/2021, Letnik:
647, Številka:
A1
Journal Article
Recenzirano
Odprti dostop
eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the primary instrument on the Spectrum-Roentgen-Gamma (SRG) mission, which was successfully launched on July 13, 2019, from the ...Baikonour cosmodrome. After the commissioning of the instrument and a subsequent calibration and performance verification phase, eROSITA started a survey of the entire sky on December 13, 2019. By the end of 2023, eight complete scans of the celestial sphere will have been performed, each lasting six months. At the end of this program, the eROSITA all-sky survey in the soft X-ray band (0.2–2.3 keV) will be about 25 times more sensitive than the ROSAT All-Sky Survey, while in the hard band (2.3–8 keV) it will provide the first ever true imaging survey of the sky. The eROSITA design driving science is the detection of large samples of galaxy clusters up to redshifts
z
> 1 in order to study the large-scale structure of the universe and test cosmological models including Dark Energy. In addition, eROSITA is expected to yield a sample of a few million AGNs, including obscured objects, revolutionizing our view of the evolution of supermassive black holes. The survey will also provide new insights into a wide range of astrophysical phenomena, including X-ray binaries, active stars, and diffuse emission within the Galaxy. Results from early observations, some of which are presented here, confirm that the performance of the instrument is able to fulfil its scientific promise. With this paper, we aim to give a concise description of the instrument, its performance as measured on ground, its operation in space, and also the first results from in-orbit measurements.
Galaxy clusters are the most massive gravitationally bound structures in the Universe. They grow by accreting smaller structures in a merging process that produces shocks and turbulence in the ...intracluster gas. We observed a ridge of radio emission connecting the merging galaxy clusters Abell 0399 and Abell 0401 with the Low-Frequency Array (LOFAR) telescope network at 140 megahertz. This emission requires a population of relativistic electrons and a magnetic field located in a filament between the two galaxy clusters. We performed simulations to show that a volume-filling distribution of weak shocks may reaccelerate a preexisting population of relativistic particles, producing emission at radio wavelengths that illuminates the magnetic ridge.
Abstract
Faraday rotation and synchrotron emission from extragalactic radio sources give evidence for the presence of magnetic fields extending over ∼ Mpc scales. However, the origin of these fields ...remains elusive. With new high-resolution grid simulations, we studied the growth of magnetic fields in a massive galaxy cluster that in several aspects is similar to the Coma cluster. We investigated models in which magnetic fields originate from primordial seed fields with comoving strengths of 0.1 nG at redshift z = 30. The simulations show evidence of significant magnetic field amplification. At the best spatial resolution (3.95 kpc), we are able to resolve the scale where magnetic tension balances the bending of magnetic lines by turbulence. This allows us to observe the final growth stage of the small-scale dynamo. To our knowledge, this is the first time that this is seen in cosmological simulations of the intracluster medium. Our mock observations of Faraday rotation provide a good match to observations of the Coma cluster. However, the distribution of magnetic fields shows strong departures from a simple Maxwellian distribution, suggesting that the three-dimensional structure of magnetic fields in real clusters may be significantly different than what is usually assumed when inferring magnetic field values from rotation measure observations.
Summary
Background
Psoriasiform and eczematous eruptions are the most common dermatological adverse reactions linked to anti‐tumour necrosis factor (TNF)‐α therapy. Yet, a detailed characterization ...of their immune phenotype is lacking.
Objectives
To characterize anti‐TNF‐α‐induced inflammatory skin lesions at a histopathological, cellular and molecular level, compared with psoriasis, eczema (atopic dermatitis) and healthy control skin.
Methods
Histopathological evaluation, gene expression (quantitative real‐time polymerase chain reaction) and computer‐assisted immunohistological studies (TissueFAXS) were performed on 19 skin biopsies from patients with inflammatory bowel disease (n = 17) and rheumatoid arthritis (n = 2) with new‐onset inflammatory skin lesions during anti‐TNF‐α‐therapy.
Results
Although most biopsies showed a psoriasiform and/or spongiotic (eczematous) histopathological architecture, these lesions were inconsistent with either psoriasis or eczema on a molecular level using an established chemokine (C‐C motif) ligand 27/inducible nitric oxide synthase classifier. Despite some differences in immune skewing depending on the specific histopathological reaction pattern, all anti‐TNF‐α‐induced lesions showed strong interferon (IFN)‐γ activation, at higher levels than in psoriasis or eczema. IFN‐γ was most likely produced by CD3/CD4/Tbet‐positive T helper 1 lymphocytes.
Conclusions
New‐onset anti‐TNF‐α‐induced eruptions previously classified as psoriasis or spongiotic dermatitis (eczema) exhibit a molecular profile that is different from either of these disorders.
What's already known about this topic?
Psoriasiform and eczematous lesions are the most common skin adverse events of anti‐tumour necrosis factor‐α treatment, yet their immune profile remains to be elucidated.
What does this study add?
We found that these lesions are distinct from genuine psoriasis and eczema, but are uniformly characterized by a strong T helper 1 inflammatory signature.
What is the translational message?
The results might help to guide future treatment strategies for chronic inflammatory diseases preventing these side‐effects in the skin.
Linked Comment: Darrigade et al. Br J Dermatol 2018; 178:1007–1008.
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Weak shocks in the intracluster medium may accelerate cosmic-ray protons and cosmic-ray electrons differently depending on the angle between the upstream magnetic field and the shock normal. In this ...work, we investigate how shock obliquity affects the production of cosmic rays in high-resolution simulations of galaxy clusters. For this purpose, we performed a magnetohydrodynamical simulation of a galaxy cluster using the mesh refinement code ENZO. We use Lagrangian tracers to follow the properties of the thermal gas, the cosmic rays and the magnetic fields over time. We tested a number of different acceleration scenarios by varying the obliquity-dependent acceleration efficiencies of protons and electrons, and by examining the resulting hadronic gamma -ray and radio emission. We find that the radio emission does not change significantly if only quasi-perpendicular shocks are able to accelerate cosmic-ray electrons. Our analysis suggests that radio-emitting electrons found in relics have been typically shocked many times before z = 0. On the other hand, the hadronic gamma -ray emission from clusters is found to decrease significantly if only quasi-parallel shocks are allowed to accelerate cosmic ray protons. This might reduce the tension with the low upper limits on gamma -ray emission from clusters set by the Fermi satellite.
Radio relics in galaxy clusters are thought to be associated with powerful shock waves that accelerate particles via diffusive shock acceleration (DSA). Among the particles accelerated by DSA, ...relativistic protons should outnumber electrons by a large factor. While the relativistic electrons emit synchrotron emission detectable in the radio band, the protons interact with the thermal gas to produce gamma-rays in hadronic interactions. Using simple models for the propagation of shock waves through clusters, the distribution of thermal gas and the efficiency of DSA, we find that the resulting hadronic gamma-ray emission lies very close or above the upper limits from the Fermi data on nearby clusters. This suggests that the relative acceleration efficiency of electrons and protons is at odds with predictions from DSA. The inclusion of re-accelerated 'fossil' particles does not seem to solve the problem. Our study highlights a possible tension of the commonly assumed scenario for the formation of radio relics and we discuss possible solutions to the problem.
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