Equilibration Processes in the Warm-Hot Intergalactic Medium

Bykov, A. M.; Paerels, F.; Petrosian, V.

doi:10.1007/s11214-008-9309-4

Cited by 47 publications

(28 citation statements)

References 39 publications

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“…In our SZ modeling we are neglecting the effect of non-equilibrium between the electrons and ions in the post-shock region. From a simple estimate based on Coulomb interaction time one can expect electron thermalization to happen over a length-scale of ∼50 kpc for a M ∼ 3 shock, but this represents an upper limit of the effect (Rudd & Nagai 2009), because it neglects energy exchange mediated by plasma instabilities which can shorten this equilibration timescale significantly (e.g., Bykov et al 2008). Following from the energy density of the relativistic particles, a nonthermal SZ contribution from the power law electrons should also be very small (Enßlin & Kaiser 2000) .…”

Section: "Negative Flux" From the Sz Effectmentioning

confidence: 99%

The impact of the SZ effect on cm-wavelength (1–30 GHz) observations of galaxy cluster radio relics

Basu

Vazza

Erler

et al. 2016

A&A

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Radio relics in galaxy clusters are believed to be associated with powerful shock fronts that originate during cluster mergers, and are a testbed for the acceleration of relativistic particles in the intracluster medium. Recently, radio relic observations have pushed into the cm-wavelength domain (1-30 GHz) where a break from the standard synchrotron power law spectrum has been found, most noticeably in the famous "Sausage" relic. Such spectral steepening is seen as an evidence for non-standard relic models, such as ones requiring seed electron population with a break in their energy spectrum. In this paper, however, we point to an important effect that has been ignored or considered insignificant while interpreting these new high-frequency radio data, namely the contamination due to the Sunyaev-Zel'dovich (SZ) effect that changes the observed synchrotron flux. Even though the radio relics reside in the cluster outskirts, the shock-driven pressure boost increases the SZ signal locally by roughly an order of magnitude. The resulting flux contamination for some well-known relics are non-negligible already at 10 GHz, and at 30 GHz the observed synchrotron fluxes can be diminished by a factor of several from their true values. At higher redshift the contamination gets stronger due to the redshift independence of the SZ effect. Interferometric observations are not immune to this contamination, since the change in the SZ signal occurs roughly at the same length scale as the synchrotron emission, although there the flux loss is less severe than single-dish observations. Besides presenting this warning to observers, we suggest that the negative contribution from the SZ effect can be regarded as one of the best evidence for the physical association between radio relics and shock waves. We present a simple analytical approximation for the synchrotron-to-SZ flux ratio, based on a theoretical radio relic model that connects the nonthermal emission to the thermal gas properties, and show that by measuring this ratio one can potentially estimate the relic magnetic fields or the particle acceleration efficiency.

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Section: "Negative Flux" From the Sz Effectmentioning

confidence: 99%

The impact of the SZ effect on cm-wavelength (1–30 GHz) observations of galaxy cluster radio relics

Basu

Vazza

Erler

et al. 2016

A&A

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“…The typical IGM temperature T ranges from 10 5 − 10 7 K (Ryu et al 2008;Bykov et al 2008). The heating rate is so high that it is incompatible with the cooling rate which is comparable to the inverse Hubble time.…”

Section: Applications In the Igm And The Host Galaxy Ismmentioning

confidence: 99%

On the Origin of the Scatter Broadening of Fast Radio Burst Pulses and Astrophysical Implications

Zhang

2016

ApJ

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Fast radio bursts (FRBs) have been identified as extragalactic sources which can make a probe of turbulence in the intergalactic medium (IGM) and their host galaxies. To account for the observed millisecond pulses caused by scatter broadening, we examine a variety of possible models of electron density fluctuations in both the IGM and the host galaxy medium. We find that a short-wave-dominated power-law spectrum of density, which may arise in highly supersonic turbulence with pronounced local dense structures of shock-compressed gas in the host interstellar medium (ISM), can produce the required density enhancements at sufficiently small scales to interpret the scattering timescale of FRBs. It implies that an FRB residing in a galaxy with efficient star formation in action tends to have a broadened pulse. The scaling of the scattering time with dispersion measure (DM) in the host galaxy varies in different turbulence and scattering regimes. The host galaxy can be the major origin of scatter broadening, but contribute to a small fraction of the total DM. We also find that the sheet-like structure of density in the host ISM associated with folded magnetic fields in a viscosity-dominated regime of magnetohydrodynamic (MHD) turbulence cannot give rise to strong scattering. Furthermore, valuable insights into the IGM turbulence concerning the detailed spatial structure of density and magnetic field can be gained from the observed scattering timescale of FRBs. Our results are in favor of the suppression of micro-plasma instabilities and the validity of collisional-MHD description of turbulence properties in the collisionless IGM.

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“…Particle acceleration by an ensemble of large scale shocks in a cluster of galaxies can create a population of non-thermal particles of sizeable pressure. This may imply a non-steady evolution of non-thermal pressure as modelled by Bykov (2001).…”

Section: Gas Heating and Entropy Production In Weak Internal Shocksmentioning

confidence: 99%

“…Multiple supernova explosions in the star forming regions (superbubbles) will additionally produce copious small scale shocks and accelerate non-thermal particles (e.g., Bykov 2001). One of the tracers for these processes can be excess metallicity in the intracluster medium, produced by the enhanced star formation period (e.g., Schindler et al 2005).…”

Section: Evidence For Shocks In Galaxy Clustersmentioning

confidence: 99%

Cosmological Shock Waves

2008

Self Cite

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Large-scale structure formation, accretion and merging processes, AGN activity produce cosmological gas shocks. The shocks convert a fraction of the energy of gravitationally accelerated flows to internal energy of the gas. Being the main gas-heating agent, cosmological shocks could amplify magnetic fields and accelerate energetic particles via the multi-fluid plasma relaxation processes. We first discuss the basic properties of standard single-fluid shocks. Cosmological plasma shocks are expected to be collisionless. We then review the plasma processes responsible for the microscopic structure of collisionless shocks. A tiny fraction of the particles crossing the shock is injected into the non-thermal energetic component that could get a substantial part of the ram pressure power dissipated at the shock. The energetic particles penetrate deep into the shock upstream producing an extended shock precursor. Scaling relations for postshock ion temperature and entropy as functions of shock velocity in strong collisionless multi-fluid shocks are discussed. We show that the multi-fluid nature of collisionless shocks results in excessive gas compression, energetic particle acceleration, precursor gas heating, magnetic field amplification and non-thermal emission. Multi-fluid shocks provide a reduced gas entropy production and could also modify the observable thermodynamic scaling relations for clusters of galaxies.

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Equilibration Processes in the Warm-Hot Intergalactic Medium

Cited by 47 publications

References 39 publications

The impact of the SZ effect on cm-wavelength (1–30 GHz) observations of galaxy cluster radio relics

The impact of the SZ effect on cm-wavelength (1–30 GHz) observations of galaxy cluster radio relics

On the Origin of the Scatter Broadening of Fast Radio Burst Pulses and Astrophysical Implications

Cosmological Shock Waves

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