10 research outputs found
Interstellar Turbulence II: Implications and Effects
Interstellar turbulence has implications for the dispersal and mixing of the
elements, cloud chemistry, cosmic ray scattering, and radio wave propagation
through the ionized medium. This review discusses the observations and theory
of these effects. Metallicity fluctuations are summarized, and the theory of
turbulent transport of passive tracers is reviewed. Modeling methods, turbulent
concentration of dust grains, and the turbulent washout of radial abundance
gradients are discussed. Interstellar chemistry is affected by turbulent
transport of various species between environments with different physical
properties and by turbulent heating in shocks, vortical dissipation regions,
and local regions of enhanced ambipolar diffusion. Cosmic rays are scattered
and accelerated in turbulent magnetic waves and shocks, and they generate
turbulence on the scale of their gyroradii. Radio wave scintillation is an
important diagnostic for small scale turbulence in the ionized medium, giving
information about the power spectrum and amplitude of fluctuations. The theory
of diffraction and refraction is reviewed, as are the main observations and
scintillation regions.Comment: 46 pages, 2 figures, submitted to Annual Reviews of Astronomy and
Astrophysic
Cosmic rays and molecular clouds
This paper deals with the cosmic-ray penetration into molecular clouds and
with the related gamma--ray emission. High energy cosmic rays interact with the
dense gas and produce neutral pions which in turn decay into two gamma rays.
This makes molecular clouds potential sources of gamma rays, especially if they
are located in the vicinity of a powerful accelerator that injects cosmic rays
in the interstellar medium. The amplitude and duration in time of the
cosmic--ray overdensity around a given source depend on how quickly cosmic rays
diffuse in the turbulent galactic magnetic field. For these reasons, gamma-ray
observations of molecular clouds can be used both to locate the sources of
cosmic rays and to constrain the properties of cosmic-ray diffusion in the
Galaxy.Comment: To appear in the proceedings of the San Cugat Forum on Astrophysics
2012, 27 pages, 10 figure
Cosmic-ray propagation and interactions in the Galaxy
Key Words energetic particles, gamma rays, interstellar medium, magnetic fields, plasmas This draft was made on January 18, 2007. We survey the theory and experimental tests for the propagation of cosmic rays in the Galaxy up to energies of 10 15 eV. A guide to the previous reviews and essential literature is given, followed by an exposition of basic principles. The basic ideas of cosmic-ray propagation are described, and the physical origin of its processes are explained. The various techniques for computing the observational consequences of the theory are described and contrasted. These include analytical and numerical techniques. We present the comparison of models with data including direct and indirect – especially gamma-ray – observations, and indicate what we can learn about cosmic-ray propagation. Some particular important topics including electrons and antiparticles are chosen for discussion