scholarly journals Cosmic ray transport in starburst galaxies

2020 ◽  
Vol 493 (2) ◽  
pp. 2817-2833 ◽  
Author(s):  
Mark R Krumholz ◽  
Roland M Crocker ◽  
Siyao Xu ◽  
A Lazarian ◽  
M T Rosevear ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Large Scale ◽  
Effective Diffusion ◽  
Cosmic Ray ◽  
Starburst Galaxies ◽  
Fine Tuning ◽  
First Principles Calculation ◽  
Streaming Instability ◽  
Γ Ray ◽  
Field Lines

ABSTRACT Starburst galaxies are efficient γ-ray producers, because their high supernova rates generate copious cosmic ray (CR) protons, and their high gas densities act as thick targets off which these protons can produce neutral pions and thence γ-rays. In this paper, we present a first-principles calculation of the mechanisms by which CRs propagate through such environments, combining astrochemical models with analysis of turbulence in weakly ionized plasma. We show that CRs cannot scatter off the strong large-scale turbulence found in starbursts, because efficient ion-neutral damping prevents such turbulence from cascading down to the scales of CR gyroradii. Instead, CRs stream along field lines at a rate determined by the competition between streaming instability and ion-neutral damping, leading to transport via a process of field line random walk. This results in an effective diffusion coefficient that is nearly energy independent up to CR energies of ∼1 TeV. We apply our computed diffusion coefficient to a simple model of CR escape and loss, and show that the resulting γ-ray spectra are in good agreement with the observed spectra of the starbursts NGC 253, M82, and Arp 220. In particular, our model reproduces these galaxies’ relatively hard GeV γ-ray spectra and softer TeV spectra without the need for any fine-tuning of advective escape times or the shape of the CR injection spectrum.

scholarly journals Cosmic ray feedback in the FIRE simulations: constraining cosmic ray propagation with GeV γ-ray emission

2019 ◽  
Vol 488 (3) ◽  
pp. 3716-3744 ◽  
Author(s):  
T K Chan ◽  
D Kereš ◽  
P F Hopkins ◽  
E Quataert ◽  
K-Y Su ◽  
...  
Keyword(s):  
Transport Coefficients ◽  
Cosmic Ray ◽  
Starburst Galaxies ◽  
Secondary Importance ◽  
Star Forming ◽  
First Results ◽  
Order Of Magnitude ◽  
Γ Ray ◽  
Field Lines ◽  
Formation Efficiency

ABSTRACT We present the implementation and the first results of cosmic ray (CR) feedback in the Feedback In Realistic Environments (FIRE) simulations. We investigate CR feedback in non-cosmological simulations of dwarf, sub-L⋆ starburst, and L⋆ galaxies with different propagation models, including advection, isotropic, and anisotropic diffusion, and streaming along field lines with different transport coefficients. We simulate CR diffusion and streaming simultaneously in galaxies with high resolution, using a two-moment method. We forward-model and compare to observations of γ-ray emission from nearby and starburst galaxies. We reproduce the γ-ray observations of dwarf and L⋆ galaxies with constant isotropic diffusion coefficient $\kappa \sim 3\times 10^{29}\, {\rm cm^{2}\, s^{-1}}$. Advection-only and streaming-only models produce order of magnitude too large γ-ray luminosities in dwarf and L⋆ galaxies. We show that in models that match the γ-ray observations, most CRs escape low-gas-density galaxies (e.g. dwarfs) before significant collisional losses, while starburst galaxies are CR proton calorimeters. While adiabatic losses can be significant, they occur only after CRs escape galaxies, so they are only of secondary importance for γ-ray emissivities. Models where CRs are ‘trapped’ in the star-forming disc have lower star formation efficiency, but these models are ruled out by γ-ray observations. For models with constant κ that match the γ-ray observations, CRs form extended haloes with scale heights of several kpc to several tens of kpc.

Evidence for Large Scale Cosmic Ray Electron Gradients in the Galaxy

1976 ◽  
Vol 3 (1) ◽  
pp. 1-6 ◽  
Author(s):  
W. R. Webber
Keyword(s):  
Large Scale ◽  
Spiral Structure ◽  
Cosmic Ray ◽  
Point Sources ◽  
Interstellar Matter ◽  
Interstellar Gas ◽  
The Galaxy ◽  
Ray Density ◽  
Γ Rays ◽  
Γ Ray

In recent years observations of γ-ray emission from the disk of the galaxy have provided a new opportunity for research into the structure of the spiral arms of our own galaxy. In Figure 1 we show a map of the structure of the disk of the galaxy as observed for γ-rays of energy > 100 MeV by the SAS-2 satellite (Fichtel et al. 1975). The angular resolution of these measurements is ~ 3°, and besides two point sources at l = 190° and 265° several features related to the spiral structure of the galaxy are evident in the data. Most of these γ-rays are believed to arise from the decay of π° mesons produced by the nuclear interactions of cosmic rays (mostly protons) with the ambient interstellar gas. As a result, the γ-ray fluxes represent a measure of the line of sight integral of the product of the cosmic ray density NCR and the interstellar matter density N1

scholarly journals Static versus Dynamical Cosmic-ray Halos

1991 ◽  
Vol 144 ◽  
pp. 359-368 ◽  
Author(s):  
Frank C. Jones
Keyword(s):  
Diffusion Coefficient ◽  
Large Scale ◽  
Cosmic Ray ◽  
Random Motion ◽  
The Galaxy ◽  
Resident Time ◽  
Ray Path ◽  
Convection Dominated ◽  
Determining Factor ◽  
Extract Information

The dynamical halo of the Galaxy offers a natural explanation for the form of the variation of cosmic-ray path length with energy. The variation above 1 GeV per nucleon can be understood as due to the variation of the diffusion coefficient, and hence the resident time in the galaxy, with energy. The flattening of the curve below 1 GeV per nucleon is seen to mark a transition to a convection dominated regime where the variation of the diffusion coefficient is no longer a determining factor. It is possible that the random motion of the cosmic rays about the galaxy that prevents us from seeing their sources in a clear manner may enable us to extract information about the galaxy at large and learn something about its large scale motions.

scholarly journals Influence of Cosmic Ray Invasions and Aerosol Plasma on Powerful Atmospheric Vortices

2019 ◽  
pp. 1-13
Author(s):  
N. I. Izhovkina ◽  
S. N. Artekha ◽  
N. S. Erokhin ◽  
L. A. Mikhailovskaya
Keyword(s):  
Cosmic Rays ◽  
Large Scale ◽  
Cosmic Ray ◽  
Winter Period ◽  
Polar Cap ◽  
Ice Storms ◽  
Large Scale Vortex ◽  
Field Lines ◽  
Plasma Vortices ◽  
Atmospheric Vortices

The Earth’s atmosphere is affected by various ionizing sources. The maximum ionization of atmospheric particles by cosmic rays corresponds to the altitude of formation of tropospheric clouds. In the high-latitude troposphere for the region of the geomagnetic polar cap, in the winter period, the excitation of local cyclonic structures are observed which are accompanied with ice storms, with invasions into middle and subtropical latitudes. The time of excitation of such cyclones is about a day that is comparable with the time of excitation of tornadoes, which are generated at low latitudes. Localization of polar cyclones is not accidental. The region of the polar cap is connected with geomagnetic field lines extended into the tail of the Earth’s magnetosphere. This area is open for the penetration of cosmic rays. The ionization of aerosols in the stratosphere and the upper troposphere by precipitating particles of cosmic rays enhances the vortex activity of the atmosphere. The important role of the aerosol impurity is manifested in the generation of plasma vortices and in the accumulation of energy and mass in the atmosphere by vortices during condensation of moisture. Due to the cascade character of the ionization process, the influence of cosmic radiation turns out to be non-linear and increases with increasing pollution of the atmosphere. Aperiodic electrostatic perturbations, which play a remarkable role in the genesis of vortices, are stochastically excited in plasma inhomogeneities. During the interaction of plasma vortices and Rossby vortices, a large-scale vortex structure is formed and grows.

scholarly journals Possible origin of the slow-diffusion region around Geminga

2019 ◽  
Vol 488 (3) ◽  
pp. 4074-4080 ◽  
Author(s):  
Kun Fang ◽  
Xiao-Jun Bi ◽  
Peng-Fei Yin
Keyword(s):  
Cosmic Ray ◽  
High Energy ◽  
Diffusion Region ◽  
Late Time ◽  
Slow Diffusion ◽  
Strong Turbulence ◽  
Streaming Instability ◽  
High Energy Electrons ◽  
Electrons And Positrons ◽  
Γ Ray

ABSTRACT Geminga pulsar is surrounded by a multiTeV γ-ray halo radiated by the high-energy electrons and positrons accelerated by the central pulsar wind nebula (PWN). The angular profile of the γ-ray emission reported by High-Altitude Water Cherenkov Observatory indicates an anomalously slow diffusion for the cosmic-ray electrons and positrons in the halo region around Geminga. In the paper we study the possible mechanism for the origin of the slow diffusion. At first, we consider the self-generated Alfvén waves due to the streaming instability of the electrons and positrons released by Geminga. However, even considering a very optimistic scenario for the wave growth, we find this mechanism does not work to account for the extremely slow diffusion at the present day, if taking the proper motion of Geminga pulsar into account. The reason is straightforward as the PWN is too weak to generate enough high-energy electrons and positrons to stimulate strong turbulence at the late time. We then propose an assumption that the strong turbulence is generated by the shock wave of the parent supernova remnant (SNR) of Geminga. Geminga may still be inside the SNR, and we find that the SNR can provide enough energy to generate the slow-diffusion circumstance. The TeV haloes around PSR B0656+14, Vela X, and PSR J1826-1334 may also be explained under this assumption.

scholarly journals Cosmic Magnetic Fields and Superconducting Strings

1990 ◽  
Vol 140 ◽  
pp. 507-512 ◽  
Author(s):  
Christopher Thompson
Keyword(s):  
Magnetic Field ◽  
Galaxy Formation ◽  
Large Scale ◽  
Cosmic Ray ◽  
String Model ◽  
Maximum Energy ◽  
Superconducting Loop ◽  
Field Lines ◽  
The Magnetic Field ◽  
A Current

A cosmic magnetic field may play a significant role in the formation of galaxies and large scale structure. In particular, a fossil field of present strength ~ 10−9 Gauss is an essential ingredient in the superconducting string model of galaxy formation (Ostriker, Thompson and Witten 1986 (OTW); Thompson 1988a). We discuss the mechanism by which a current is induced on a superconducting string, including recent work on the reconnection of magnetic field lines near the string (Kulsrud and Thompson 1989). A substantial amount of baryonic plasma is trapped on the magnetic field lines which close around the string. The current on a loop almost certainly does not undergo exponential dynamo amplification; an oscillating superconducting loop emits a relativistic MHD wind (Thompson 1988a). Decaying superconducting loops fill most of the intergalactic medium with a relativistic, magnetized fluid. In this model, the gas between galaxies is highly clumped and strongly magnetized, the field strength approaching 1 μG. The maximum energy of cosmic ray protons accelerated at string-driven shocks is ~ 1020 eV (Madau and Thompson 1989).

scholarly journals Role of cosmic-ray streaming and turbulent damping in driving galactic winds

2019 ◽  
Vol 490 (1) ◽  
pp. 1271-1282 ◽  
Author(s):  
F Holguin ◽  
M Ruszkowski ◽  
A Lazarian ◽  
R Farber ◽  
H-Y K Yang
Keyword(s):  
Large Scale ◽  
Formation Rate ◽  
Cosmic Ray ◽  
High Energy ◽  
Galactic Cosmic Rays ◽  
Mass Loading ◽  
Local Magnetization ◽  
Streaming Instability ◽  
Galactic Winds ◽  
Turbulent Damping

ABSTRACT Large-scale galactic winds driven by stellar feedback are one phenomenon that influences the dynamical and chemical evolution of a galaxy, redistributing material throughout the circumgalatic medium. Non-thermal feedback from galactic cosmic rays (CRs) – high-energy charged particles accelerated in supernovae and young stars – can impact the efficiency of wind driving. The streaming instability limits the speed at which they can escape. However, in the presence of turbulence, the streaming instability is subject to suppression that depends on the magnetization of turbulence given by its Alfvén Mach number. While previous simulations that relied on a simplified model of CR transport have shown that super-Alfvénic streaming of CRs enhances galactic winds, in this paper we take into account a realistic model of streaming suppression. We perform three-dimensional magnetohydrodynamic simulations of a section of a galactic disc and find that turbulent damping dependent on local magnetization of turbulent interstellar medium (ISM) leads to more spatially extended gas and CR distributions compared to the earlier streaming calculations, and that scale heights of these distributions increase for stronger turbulence. Our results indicate that the star formation rate increases with the level of turbulence in the ISM. We also find that the instantaneous wind mass loading is sensitive to local streaming physics with the mass loading dropping significantly as the strength of turbulence increases.

scholarly journals Turbulence-level dependence of cosmic ray parallel diffusion

2020 ◽  
Vol 498 (4) ◽  
pp. 5051-5064 ◽  
Author(s):  
P Reichherzer ◽  
J Becker Tjus ◽  
E G Zweibel ◽  
L Merten ◽  
M J Pueschel
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Coefficients ◽  
Cosmic Ray ◽  
Resonant Scattering ◽  
Homogeneous Magnetic Field ◽  
Resonant Interaction ◽  
Turbulence Level ◽  
Parallel Diffusion ◽  
Low Energies ◽  
Field Lines

ABSTRACT Understanding the transport of energetic cosmic rays belongs to the most challenging topics in astrophysics. Diffusion due to scattering by electromagnetic fluctuations is a key process in cosmic ray transport. The transition from a ballistic to a diffusive-propagation regime is presented in direct numerical calculations of diffusion coefficients for homogeneous magnetic field lines subject to turbulent perturbations. Simulation results are compared with theoretical derivations of the parallel diffusion coefficient’s dependences on the energy and the fluctuation amplitudes in the limit of weak turbulence. The present study shows that the widely used extrapolation of the energy scaling for the parallel diffusion coefficient to high turbulence levels predicted by quasi-linear theory does not provide a universally accurate description in the resonant-scattering regime. It is highlighted here that the numerically calculated diffusion coefficients can be polluted for low energies due to missing resonant interaction possibilities of the particles with the turbulence. Five reduced-rigidity regimes are established, which are separated by analytical boundaries derived in this work. Consequently, a proper description of cosmic ray propagation can only be achieved by using a turbulence-level-dependent diffusion coefficient and can contribute to solving the Galactic cosmic ray gradient problem.

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