Abstract
We use hydrodynamical simulations in a $(256\;pc)^3$ periodic box to
model the impact of supernova (SN) explosions on the multi-phase interstellar
medium (ISM) for initial densities $n =$ 0.5-30 cm$^-3$ and SN rates 1-720
Myr$^-1$. We include radiative cooling, diffuse heating, and the formation of
molecular gas using a chemical network. The SNe explode either at random
positions, at density peaks, or both. We further present a model combining
thermal energy for resolved and momentum input for unresolved SN remnants.
Random driving at high SN rates results in hot gas ($T10^6$ K) filling
$> 90$% of the volume. This gas reaches high pressures ($10^4 < P/k_B
< 10^7$ K cm$^-3$) due to the combination of SN explosions in the hot, low
density medium and confinement in the periodic box. These pressures move the
gas from a two-phase equilibrium to the single-phase, cold branch of the
cooling curve. The molecular hydrogen dominates the mass ($>50$%), residing in
small, dense clumps. Such a model might resemble the dense ISM in high-redshift
galaxies. Peak driving results in huge radiative losses, but disrupts the
densest regions by construction, producing a filamentary ISM with virtually no
hot gas, and a small molecular hydrogen mass fraction ($1$%). Varying the
ratio of peak to random SNe yields ISM properties in between the two extremes,
with a sharp transition for equal contributions (at $n = 3$ cm$^-3$). Modern
galaxies have few SNe in density peak locations due to preceding stellar winds
and ionisation. The velocity dispersion in HI remains $10$ km s$^-1$
in all cases. For peak driving the velocity dispersion in H$_\alpha$ can be as
high as $70$ km s$^-1$ due to the contribution from young, embedded SN
remnants.
Description
[1411.0009] Modelling the supernova-driven ISM in different environments
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