arXiv subjects

Alexei G. Kritsuk

Publications and source records attributed to Alexei G. Kritsuk.

39 records · Page 3Linked to original sources

arXiv2002

Interstellar Phase Transitions Stimulated by Time-dependent Heating

We use three-dimensional hydrodynamic numerical simulations to study phase transformations occurring in a clumpy interstellar gas exposed to time-dependent volumetric heating. To mimic conditions in the Galactic interstellar medium, we take a numerical model of a turbulent multiphase medium from Kritsuk & Norman (2002) computed in a periodic box with mean density n_0=0.25 cm^-3 and mean pressure P_0/k~10^3.4 K cm^-3. A second model with n_0=1 cm^-3 is also considered. Variations of the heating rate on a timescale of 1-10 Myr applied thereafter cause pressure variations in the gas and shifting of the thermal equilibrium curve in the phase plane. This stimulates mass transfer between the gas phases via thermal instability, converting 5-10% of the thermal energy into kinetic energy of gas motions. The experiments demonstrate that recurrent substantial heating episodes can maintain turbulence at this level. Possible applications to the interstellar gas heated by variable far-ultraviolet background radiation produced by short-living massive stars are discussed.

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arXiv2002

Thermal Instability-Induced Interstellar Turbulence

We study the dynamics of phase transitions in the interstellar medium by means of three-dimensional hydrodynamic numerical simulations. We use a realistic cooling function and generic nonequilibrium initial conditions to follow the formation history of a multiphase medium in detail in the absence of gravity. We outline a number of qualitatively distinct stages of this process, including a linear isobaric evolution, transition to an isochoric regime, formation of filaments and voids (also known as "thermal" pancakes), the development and decay of supersonic turbulence, an approach to pressure equilibrium, and final relaxation of the multiphase medium. We find that 1%-2% of the initial thermal energy is converted into gas motions in one cooling time. The velocity field then randomizes into turbulence that decays on a dynamical timescale E_k ~ t^-n, 1 < n < 2. While not all initial conditions yield a stable two-phase medium, we examine such a case in detail. We find that the two phases are well mixed with the cold clouds possessing a fine-grained structure near our numerical resolution limit. The amount of gas in the intermediate unstable phase roughly tracks the rms turbulent Mach number, peaking at 25% when M_rms ~ 8, decreasing to 11% when M_rms ~ 0.4.

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arXiv1996

On the Fundamental Properties of Dynamically Hot Galaxies

A two-component isothermal equilibrium model is applied to reproduce basic structural properties of dynamically hot stellar systems immersed in their massive dark haloes. The origin of the fundamental plane relation for giant ellipticals is naturally explained as a consequence of dynamical equilibrium in the context of the model. The existence of two galactic families displaying different behaviour in the luminosity--surface-brightness diagram is shown to be a result of a smooth transition from dwarfs, dominated by dark matter near the centre, to giants dominated by the luminous stellar component. The comparison of empirical scaling relations with model predictions suggests that probably a unique dissipative process was operating during the violent stage of development of stellar systems in the dark haloes, and the depth of the potential well controlled the observed luminosity of the resulting galaxies. The interpretation also provides some restrictions on the properties of dark haloes implied by the fundamental scaling laws.

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