A Supernova-regulated Interstellar Medium: Simulations of the Turbulent Multiphase Medium

Abstract

The dynamic state of the interstellar medium, heated and stirred by supernovae (SNe), is simulated using a three-dimensional, nonideal MHD model in a domain extended kpc horizontally and 2 kpc vertically, 0.5 # 0.5 with the gravitational field symmetric about the midplane of the domain, . We include both Type I and z ϭ 0 Type II SNe, allowing the latter to cluster in regions with enhanced gas density. The system segregates into two main phases: a warm, denser phase and a hot, dilute gas in global pressure equilibrium; there is also dense, cool gas compressed into filaments, shells, and clumps by expanding SN remnants. The filling factor of the hot phase grows with height, so it dominates at kpc. The multicomponent structure persists throughout the FzF տ 0.5 simulation, and its statistical parameters show little time variation. The warm gas is in hydrostatic equilibrium, which is supported by thermal and turbulent pressures. The multiphase gas is in a state of developed turbulence. The rms random velocity is different in the warm and hot phases, 10 and 40 km s Ϫ1 , respectively, at FzF Շ 1 kpc; the turbulent cell size (twice the velocity correlation scale) is about 60 pc in the warm phase.

Volume filling factors of the ISM phases in star forming galaxies

“…Thus, Ferrière's model does in fact not resolve the vertical gas transport, and hence misses out on the volume fraction of a considerable amount of gas, leading effectively to an increase with z-height above 1 kpc as described here. Figure 2 of Korpi et al (1999) shows the temperature, density and P/k PDFs for different volumes of the disk: |z| < 0.25, |z| < 0.5, and |z| < 1 kpc. These are averaged volume-weighted histograms calculated over a period of 50 Myr using six snapshots at equal time intervals between 20 and 70 Myr of evolution.…”

“…Attempts to determine the occupation fraction of the different phases, and in particular of the hot gas, by means of modelling the effects of SNe and SBs in the ISM, have been carried out by several authors (e.g., Ferrière 1995Ferrière , 1998Korpi et al 1999). However, these models do not include the circulation of gas between the disk and the full halo, thus being unable to resolve the high-z region; neither do they take into account the mixing between the different phases.…”

Nonlinear magnetic diffusion and magnetic helicity transport in galactic dynamos

“…We emphasize that direct numerical simulations of interstellar turbulence (see e.g. Korpi et al 1999), followed by estimations of the appropriate mean-field dynamo control parameters, are very desirable and even essential in this context.…”

Turbulent Dissipation in the Interstellar Medium: The Coexistence of Forced and Decaying Regimes and Implications for Galaxy Formation and Evolution

“…Indeed, numerical simulations show that up to 5%È10% of the energy produced by SNe can be transformed into kinetic energy in the extreme case of multiple SN explosions forming supershells (e.g., Silich et al 1996 ;Korpi et al 1999) ; for isolated SNe, this fraction is lower than D1%.…”

“…Results from thermohydrodynamic simulations in di †erent contexts have shown that the kinetic energy injected by SNe and massive stars E k to the ISM deeply a †ects the dynamics of the gas in disk galaxies, causing it to be highly turbulent (e.g., Bania & 645 Vol. 553 Lyon 1980 ;Chiang & Prendergast 1985 ;Chiang & Bregman 1988 ;Navarro & White 1993 ;Mihos & Hernquist 1994, 1996Rosen & Bregman 1995 ;Vazquezet al 1995 ;Friedli & Benz 1995 ;Passot, Semadeni & Pouquet 1995 ;Gerritsen 1997 ;Vazquez-Semadeni, Avillez 2000 ;Korpi et al 1999 ; see also the reviews by Scalo 1987 andby et al 2000b). Cloud formaVazquez-Semadeni tion and disruption, the structure and dynamics of the vertical gaseous disk (in particular its scale height), fountains and chimneys, and even a huge hot gas corona (the "" intrahalo medium ÏÏ) in virial equilibrium (including the potential of a huge cosmological dark matter halo), might be some of the phenomena and processes related to the turbulence produced by stellar kinetic energy sources.…”