Cold Exponential Disks From Interstellar Fountains

Abstract

We present the results of a simple numerical model with phenomenological cloud growth and explosive disruption processes, and with fountain launched ballistic motions of disrupted cloud fragments out of the disk. These processes generate an effective scattering of gas elements over much larger distances than noncircular impulses in the plane, which are quickly damped. The result is evolution of the global cloud density profile to an exponential form on a roughly Gyr timescale. This is consistent with our previous results on the effects of star scattering o? massive clumps in young disks, and gas holes in dwarf galaxies. However, in those cases the scattering processes generated thick, warm/hot stellar disks. Here we find that the exponential gas disks remain cold. Star formation in this gas would produce a thin exponential stellar disk.

4 pages, 3 figures, accepted for ApJ Letters

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• Power-law Sersic profiles in hydrostatic stellar galaxy discs
• Exponential galaxy discs as the quasi-stationary distribution in a Markov chain model simulating stellar scattering
• The impact of radial migration on disk galaxy star formation histories: II. Role of bar strength, disk thickness, and merger history