The microphysics and macrophysics of cosmic rays

Zweibel, Ellen G.

doi:10.1063/1.4807033

Cited by 169 publications

(153 citation statements)

References 103 publications

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“…In this picture, CRs scatter on waves excited by the streaming instability (Kulsrud & Pearce 1969;Wentzel 1974;Zweibel 2013). In a state of marginally stable anisotropy, the CRs stream at the Alfvén speed down their pressure gradients.…”

Section: Streaming Of Crsmentioning

confidence: 99%

“…In the latter case, CRs stream down their pressure gradients along magnetic field lines at (or above) the Alfvén speed. In this case, CRs experience an effective drag force that heats the gas (Zweibel 2013). This Alfvén wave heating was proposed as a viable mechanism to offset radiative cooling (Loewenstein et al 1991;Guo & Oh 2008;Pfrommer 2013;Jacob & Pfrommer 2016a.…”

Section: Introductionmentioning

confidence: 99%

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Cosmic-Ray Feedback Heating of the Intracluster Medium

Ruszkowski

Yang

Reynolds

2017

ApJ

111

112

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Active galactic nuclei (AGNs) play a central role in solving the decades-old cooling-flow problem. Although there is consensus that AGNs provide the energy to prevent catastrophically large star formation, one major problem remains: How is the AGN energy thermalized in the intracluster medium (ICM)? We perform a suite of threedimensional magnetohydrodynamical adaptive mesh refinement simulations of AGN feedback in a cool core cluster including cosmic rays (CRs). CRs are supplied to the ICM via collimated AGN jets and subsequently disperse in the magnetized ICM via streaming, and interact with the ICM via hadronic, Coulomb, and streaming instability heating. We find that CR transport is an essential model ingredient at least within the context of the physical model considered here. When streaming is included, (i) CRs come into contact with the ambient ICM and efficiently heat it, (ii) streaming instability heating dominates over Coulomb and hadronic heating, (iii) the AGN is variable and the atmosphere goes through low-/high-velocity dispersion cycles, and, importantly, (iv) CR pressure support in the cool core is very low and does not demonstrably violate observational constraints. However, when streaming is ignored, CR energy is not efficiently spent on the ICM heating and CR pressure builds up to a significant level, creating tension with the observations. Overall, we demonstrate that CR heating is a viable channel for the AGN energy thermalization in clusters and likely also in ellipticals, and that CRs play an important role in determining AGN intermittency and the dynamical state of cool cores.

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Section: Streaming Of Crsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Cosmic-Ray Feedback Heating of the Intracluster Medium

Ruszkowski

Yang

Reynolds

2017

ApJ

111

112

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“…Hennebelle & Chabrier (2008, 2013 (hereafter HC) and Hopkins (2012aHopkins ( ,b, 2013a) have developed models for the scale-dependent density structure in turbulent media, inspired by the Press-Schechter (Press & Schechter 1974) and excursion set (Bond et al 1991) formalisms first applied in the context of cosmology. The basic goal of these models is to derive a PDF for the logarithmic density s after it has been smoothed to an arbitrary size scale .…”

Section: Why Is the Scaling Ofmentioning

confidence: 99%

“…One can define a length scale for the dissipation associated with ambipolar diffusion just as one can for viscous dissipation (Balsara 1996;Zweibel & Brandenburg 1997;Zweibel 2002;Li et al 2006aTilley & Balsara 2011),…”

Section: Characteristic Numbersmentioning

confidence: 99%

The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function

2014

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Star formation lies at the center of a web of processes that drive cosmic evolution: generation of radiant energy, synthesis of elements, formation of planets, and development of life. Decades of observations have yielded a variety of empirical rules about how it operates, but at present we have no comprehensive, quantitative theory. In this review I discuss the current state of the field of star formation, focusing on three central questions: what controls the rate at which gas in a galaxy converts to stars? What determines how those stars are clustered, and what fraction of the stellar population ends up in gravitationally-bound structures? What determines the stellar initial mass function, and does it vary with star-forming environment? I use these three question as a lens to introduce the basics of star formation, beginning with a review of the observational phenomenology and the basic physical processes. I then review the status of current theories that attempt to solve each of the three problems, pointing out links between them and opportunities for theoretical and numerical work that crosses the scale between them. I conclude with a discussion of prospects for theoretical progress in the coming years.

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“…This fluid approximation is justified because CRs are confined by the magnetic field and well scattered by small scale mag-⋆ E-mail: kudoyk.aplab@chiba-u.jp (YK) netic fluctuations (see e.g. Zweibel 2013). CRs are assumed to be an ultrarelativistic gas and hence the pressure is assumed to be one third of the energy density in the CR MHD equations.…”

Section: Introductionmentioning

confidence: 99%

Approximate Riemann solvers for the cosmic ray magnetohydrodynamical equations

Kudoh

Hanawa

2016

Mon. Not. R. Astron. Soc.

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We analyze the cosmic-ray magnetohydrodynamic (CR MHD) equations to improve the numerical simulations. We propose to solve them in the fully conservation form, which is equivalent to the conventional CR MHD equations. In the fully conservation form, the CR energy equation is replaced with the CR "number" conservation, where the CR number density is defined as the three fourths power of the CR energy density. The former contains an extra source term, while latter does not. An approximate Riemann solver is derived from the CR MHD equations in the fully conservation form. Based on the analysis, we propose a numerical scheme of which solutions satisfy the Rankine-Hugoniot relation at any shock. We demonstrate that it reproduces the Riemann solution derived by Pfrommer et al. (2006) for a 1D CR hydrodynamic shock tube problem. We compare the solution with those obtained by solving the CR energy equation. The latter solutions deviate from the Riemann solution seriously, when the CR pressure dominates over the gas pressure in the post-shocked gas. The former solutions converge to the Riemann solution and are of the second order accuracy in space and time. Our numerical examples include an expansion of high pressure sphere in an magnetized medium. Fast and slow shocks are sharply resolved in the example. We also discuss possible extension of the CR MHD equations to evaluate the average CR energy.

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The microphysics and macrophysics of cosmic rays

Cited by 169 publications

References 103 publications

Cosmic-Ray Feedback Heating of the Intracluster Medium

Cosmic-Ray Feedback Heating of the Intracluster Medium

The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function

Approximate Riemann solvers for the cosmic ray magnetohydrodynamical equations

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