Mesoscale Flows in Multiphase Hydrodynamic Models of Galaxy Disks

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Session 48 -- Spiral, Dwarf and Irregular Galaxies
Display presentation, Wednesday, 1, 1994, 9:20-6:30

[48.18] Mesoscale Flows in Multiphase Hydrodynamic Models of Galaxy Disks

Curtis Struck-Marcell (Iowa State)

Interstellar gas dynamics in late-type galaxy disks is simulated using a Smooth Particle Hydrodynamics code, which includes the effects of local self-gravity, a simple cooling function and heat input for a finite duration in regions where a threshold density for star formation is exceeded. The model disks are initialized at a constant temperature and at a density near the critical value for gravitational instability. Relatively dense clouds form, exceed the star formation threshold and are heated. The disks then relax to a state where the cool gas is concentrated in a thin layer enveloped by hot gas with a larger vertical scale height. The heating causes the formation of local bubbles and fountain flows throughout much of the disk. When the heating timescale is sufficiently (but not unreasonably) long, a vertically circulating flow can develop in the central regions. In this flow gas heated in an extended starburst, driven by a weak asymmetric bar rises out of the disk at velocities of order 100 km/s. Opposite the dominant side of the bar, previously heated gas has cooled, and falls back into the disk. The weak bar extends out to a radius where the vertical epicyclic period equals half a circular rotation period. Typical energies of this phenomena are intermediate between those characteristic of disk superbubbles and those of superwinds resulting from nuclear starbursts. In contrast to these latter flows, and in the absence of gas consumption, this "mesowind" is long-lived.

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