Dynamical Effects of Global Thermal Instability in Shock‐compressed Gas Slabs

Yamada, Masako; Nishi, Ryoichi

doi:10.1086/318329

Cited by 6 publications

(7 citation statements)

References 37 publications

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“…Furthermore, clouds in the ISM are intrinsically turbulent as they emerge from the non-isotropic condensation of thermally-unstable gas (e.g., see Field 1965;Yamada & Nishi 2001;van Loo et al 2007;van Loo, Falle & Hartquist 2010;Inoue & Inutsuka 2012;Proga & Waters 2015), or from thin shell instabilities in colliding winds (e.g., see Stevens, Blondin & Pollock 1992, Dgani, Walder & Nussbaumer 1993, Vishniac 1994, Parkin et al 2011, Calderón et al 2016. Observational and numerical studies of clumpy media show, for example, that the density profiles inside clouds are best described by log-normal distributions in supersonic, transonic, and subsonic scenarios (e.g., see Vazquez-Semadeni 1994;Passot & Vázquez-Semadeni 1998;Nordlund & Padoan 1999;Federrath, Klessen & Schmidt 2008;Kainulainen et al 2009;Federrath et al 2010;Kainulainen et al 2014;Schneider et al 2012Schneider et al , 2013Schneider et al , 2016.…”

Section: Relevance Of This Studymentioning

confidence: 99%

Filament formation in wind–cloud interactions– II. Clouds with turbulent density, velocity, and magnetic fields

Banda-Barragán

Federrath

Crocker

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We present a set of numerical experiments designed to systematically investigate how turbulence and magnetic fields influence the morphology, energetics, and dynamics of filaments produced in wind-cloud interactions. We cover three-dimensional, magnetohydrodynamic systems of supersonic winds impacting clouds with turbulent density, velocity, and magnetic fields. We find that log-normal density distributions aid shock propagation through clouds, increasing their velocity dispersion and producing filaments with expanded cross sections and highly-magnetised knots and sub-filaments. In self-consistently turbulent scenarios the ratio of filament to initial cloud magnetic energy densities is ∼ 1. The effect of Gaussian velocity fields is bound to the turbulence Mach number: Supersonic velocities trigger a rapid cloud expansion; subsonic velocities only have a minor impact. The role of turbulent magnetic fields depends on their tension and is similar to the effect of radiative losses: the stronger the magnetic field or the softer the gas equation of state, the greater the magnetic shielding at wind-filament interfaces and the suppression of Kelvin-Helmholtz instabilities. Overall, we show that including turbulence and magnetic fields is crucial to understanding cold gas entrainment in multi-phase winds. While cloud porosity and supersonic turbulence enhance the acceleration of clouds, magnetic shielding protects them from ablation and causes Rayleigh-Taylor-driven sub-filamentation. Wind-swept clouds in turbulent models reach distances ∼ 15 − 20 times their core radius and acquire bulk speeds ∼ 0.3 − 0.4 of the wind speed in one cloud-crushing time, which are three times larger than in non-turbulent models. In all simulations the ratio of turbulent magnetic to kinetic energy densities asymptotes at ∼ 0.1 − 0.4, and convergence of all relevant dynamical properties requires at least 64 cells per cloud radius.

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Section: Relevance Of This Studymentioning

confidence: 99%

Filament formation in wind–cloud interactions– II. Clouds with turbulent density, velocity, and magnetic fields

Banda-Barragán

Federrath

Crocker

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…Balbus 1986; Balbus & Soker 1989; Balbus 1995), global TI by linear perturbation analysis (e.g. Yamada & Nishi 2001) and numerical hydrodynamical calculations to investigate the perturbations in the non‐linear regime (e.g. Hattori & Habe 1990).…”

Section: Introductionmentioning

confidence: 99%

Multiphase, non-spherical gas accretion on to a black hole

Barai¹,

Proga²,

Nagamine³

2012

Monthly Notices of the Royal Astronomical Society

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We investigate non‐spherical behaviour of gas accreting on to a central supermassive black hole. Assuming optically thin conditions, we include radiative cooling and radiative heating by the central X‐ray source. Our simulations are performed using the 3D smoothed particle hydrodynamic (SPH) code gadget‐3 and are compared to theoretical predictions as well as to 1D simulations performed using the grid code zeus. As found in earlier 1D studies, our 3D simulations show that the accretion mode depends on the X‐ray luminosity (LX) for a fixed density at infinity and accretion efficiency. In the low LX limit, gas accretes in a stable, spherically symmetric fashion. In the high LX limit, the inner gas is significantly heated up and expands, reducing the central mass inflow rate. The expanding gas can turn into a strong enough outflow capable of expelling most of the gas at larger radii. For some intermediate LX, the accretion flow becomes unstable developing prominent non‐spherical features. Our detailed analysis and tests show that the key reason for this unstable non‐spherical nature of the flow is thermal instability (TI). Small perturbations of the initially spherically symmetric accretion flow that is heated by the intermediate LX quickly grow to form cold and dense clumps surrounded by overheated low‐density regions. The cold clumps continue their inwards motion forming filamentary structures, while the hot infalling gas slows down because of buoyancy and can even start outflowing through the channels in between the filaments. We measured various local and global properties of our solutions. In particular, we found that the ratio between the mass inflow rates of the cold and hot gas is a dynamical quantity depending on several factors: time, spatial location and LX; and ranges between 0 and 4. We briefly discuss astrophysical implications of such TI‐driven fragmentation of accreting gas on the formation of clouds in narrow‐ and broad‐line regions of active galactic nuclei, the formation of stars and the observed variability of the active galactic nuclei luminosity.

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“…Recently, Yamada & Nishi (2001) investigated the stability properties of shock-compressed gas slabs by introducing a cold layer of finite thickness. They considered both symmetric and antisymmetric modes and reported the existence of quasi-oscillatory modes, in addition to the overstable ones.…”

Section: Introductionmentioning

confidence: 99%

The Dynamics of Radiative Shock Waves: Linear and Nonlinear Evolution

Mignone

2005

ApJ

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The stability properties of one-dimensional radiative shocks with a power-law cooling function of the form Ã / 2 T are the main subject of this work. The linear analysis originally presented by Chevalier & Imamura is thoroughly reviewed for several values of the cooling index and higher overtone modes. Consistently with previous results, it is shown that the spectrum of the linear operator consists of a series of modes with increasing oscillation frequency. For each mode a critical value of the cooling index, c , can be defined so that modes with < c are unstable while modes with > c are stable. The perturbative analysis is complemented by several numerical simulations to follow the time-dependent evolution of the system for different values of . Particular attention is given to the comparison between numerical and analytical results (during the early phases of the evolution) and to the role played by different boundary conditions. It is shown that an appropriate treatment of the lower boundary yields results that closely follow the predicted linear behavior. During the nonlinear regime, the shock oscillations saturate at a finite amplitude and tend to a quasi-periodic cycle. The modes of oscillations during this phase do not necessarily coincide with those predicted by linear theory but may be accounted for by modemode coupling.

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Dynamical Effects of Global Thermal Instability in Shock‐compressed Gas Slabs

Cited by 6 publications

References 37 publications

Filament formation in wind–cloud interactions– II. Clouds with turbulent density, velocity, and magnetic fields

Filament formation in wind–cloud interactions– II. Clouds with turbulent density, velocity, and magnetic fields

Multiphase, non-spherical gas accretion on to a black hole

The Dynamics of Radiative Shock Waves: Linear and Nonlinear Evolution

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