Thermal Properties of Interstellar Gas Heated by Cosmic Rays

Goldsmith, Donald; Habing, H. J.; Field, George B.

doi:10.1086/150181

Cited by 67 publications

(23 citation statements)

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“…In all cases, the sum + µ -( ) ( ) K k M k k 3 2 at this resolution and the scaling range for the sum is longer than that for any of the two components. 6 Here, as in the case of kinetic energy spectral density, the cospectrum r form of induced turbulent magnetic energy, which tends to saturate at equipartition with the kinetic energy on small scales. Due to the Alfvén effect, a strong dynamic field alignment develops in the quasi-stationary state in most of the computational domain, at characteristic ISM densities ∼1 cm −3 .…”

Section: Discussionmentioning

confidence: 95%

“…Interstellar turbulence, however, differs from the familiar Kolmogorov homogeneous and isotropic incompressible case [2,3] in several important respects: it is neither isotropic nor homogeneous [4]; the interstellar gas is highly compressible and magnetized; and its thermal energy is not strictly conserved. Instead, the ISM-specific radiative cooling and volumetric heating functions determine an equilibrium multiphase nature of the neutral ISM [5][6][7]. Nonlinear advection couples with nonlinear radiative cooling, further complicating the treatment of the ISM.…”

Section: Introductionmentioning

confidence: 99%

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The structure and statistics of interstellar turbulence

2017

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We explore the structure and statistics of multiphase, magnetized ISM turbulence in the local Milky Way by means of driven periodic box numerical MHD simulations. Using the higher order-accurate piecewise-parabolic method on a local stencil (PPML), we carry out a small parameter survey varying the mean magnetic field strength and density while fixing the rms velocity to observed values. We quantify numerous characteristics of the transient and steady-state turbulence, including its thermodynamics and phase structure, kinetic and magnetic energy power spectra, structure functions, and distribution functions of density, column density, pressure, and magnetic field strength. The simulations reproduce many observables of the local ISM, including molecular clouds, such as the ratio of turbulent to mean magnetic field at 100 pc scale, the mass and volume fractions of thermally stable HI, the lognormal distribution of column densities, the mass-weighted distribution of thermal pressure, and the linewidth-size relationship for molecular clouds. Our models predict the shape of magnetic field probability density functions (PDFs), which are strongly non-Gaussian, and the relative alignment of magnetic field and density structures. Finally, our models show how the observed low rates of star formation per free-fall time are controlled by the multiphase thermodynamics and largescale turbulence.To explore this complexity, we develop self-consistent models based on very idealized numerical experiments, linking together scales relevant to molecular cloud formation and fragmentation. We exploit the concept of self-organization in nonequilibrium nonlinear dissipative systems [14] in application to the ISM, which is long overdue [15]. We treat interstellar turbulence as an agent that imposes 'order' in the form of coherent structures and correlations between flow fields emerging in a simple periodic box simulation when a statistically stationary state fully develops. In this case, the details of initial conditions are no longer important. Instead the steady state provides realistic initial conditions for star formation. Unlike various flavors of the popular converging flow scenario [16][17][18][19], this approach allows us to reproduce basic ISM observables, including properties of local molecular clouds, with only a few control parameters. The model can be readily extended to include more physics (e.g., radiative transfer and chemistry), to augment the range of resolved scales, and to close the star formation feedback loop.The paper is organized as follows. Section 2 contains the details of our numerical models, including equations, initial and boundary conditions, and parameters. Section 3 presents the results of statistical analysis and comparison with observations for a number of ISM diagnostics. Section 3.1 describes the transition to turbulence and global properties of the statistically stationary state. Section 3.2 summarizes the evolution of magnetic field under the action of random large-scale external forcing. In section 3...

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Section: Discussionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

The structure and statistics of interstellar turbulence

2017

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“…This latter reflects the non-adiabatic processes included through the heating and cooling function Γ(ρ) and Λ(ρ, T ). At low temperature ISM (T < 10 4 K), the heating is dominated by the cosmic ray heating (Goldsmith et al 1969) and by the photo-electric UV heating on grains (Watson 1972;Draine 1978). As soon as the gas is enriched with metals, the cooling function is dominated by the CII, SiII, OI, FeII line emissions (Maio et al 2007).…”

Section: The Straightforward Approachmentioning

confidence: 99%

Simulations of galactic disks including a dark baryonic component

Revaz¹,

Pfenniger²,

Combes³

et al. 2009

A&A

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The near proportionality between HI and dark matter in outer galactic disks prompted us to run N-body simulations of galactic disks in which the observed gas content is supplemented by a dark gas component representing between zero and five times the visible gas content. While adding baryons in the disk of galaxies may solve some issues, it poses the problem of disk stability. We show that the global stability is ensured if the ISM is multiphased, composed of two partially coupled phases, a visible warm gas phase and a weakly collisionless cold dark phase corresponding to a fraction of the unseen baryons. The phases are subject to stellar and UV background heating and gas cooling, and their transformation into each other is studied as a function of the coupling strength. This new model, which still possesses a dark matter halo, fits the rotation curves as well as the classical CDM halos, but is the only one to explain the existence of an open and contrasting spiral structure, as observed in the outer HI disks

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“…Interstellar turbulence.-The interstellar medium (ISM) is a complex magnetized mix of neutral and ionized gas, dust, cosmic rays, and radiation, all coupled through mass, energy, and momentum exchange. The conducting fluid component, including neutral and ionized hydrogen, is thermally unstable in certain density and temperature regimes [3] and tends to split into two or more stable thermal phases [4,5]. The ISM is also constantly energized by supernova explosions and other relevant sources in the Galactic disk, which keep the fluid turbulent [6,7].…”

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confidence: 99%

Dust-Polarization Maps for Local Interstellar Turbulence

2018

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We show that simulations of magnetohydrodynamic turbulence in the multiphase interstellar medium yield an E/B ratio for polarized emission from Galactic dust in broad agreement with recent Planck measurements. In addition, the B-mode spectra display a scale dependence that is consistent with observations over the range of scales resolved in the simulations. The simulations present an opportunity to understand the physical origin of the E/B ratio and a starting point for more refined models of Galactic emission of use for both current and future cosmic microwave background experiments.

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Thermal Properties of Interstellar Gas Heated by Cosmic Rays

Cited by 67 publications

References 0 publications

The structure and statistics of interstellar turbulence

The structure and statistics of interstellar turbulence

Simulations of galactic disks including a dark baryonic component

Dust-Polarization Maps for Local Interstellar Turbulence

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