EDP Sciences
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Volume 423, Number 1, August III 2004
Page(s) 183 - 188
Section Galactic structure, stellar clusters and populations
DOI http://dx.doi.org/10.1051/0004-6361:20047141

A&A 423, 183-188 (2004)
DOI: 10.1051/0004-6361:20047141

A mushroom-shaped structure from the impact of a cloud with the Galactic disk

Takahiro Kudoh and Shantanu Basu

Department of Physics and Astronomy, University of Western Ontario, London, Ontario N6A 3K7, Canada
    e-mail: kudoh@astro.uwo.ca

(Received 26 January 2004 / Accepted 3 May 2004)

We propose that the mushroom-shaped structure of the Galactic worm GW 123.4-1.5 is created by a cloud collision with the Galactic gas disk. A hydrodynamic simulation shows that a mushroom-shaped structure is created after the cloud crosses the Galactic midplane. The lifetime of the mushroom-shaped structure is of order the dynamical time scale of the disk, ${\sim} 10^7$ years. We find that the velocities across the cap of the mushroom-shaped structure in the simulation are consistent with the observed values. The simulation also predicts a structure on the opposite side of the Galactic plane which is created by the Kelvin-Helmholtz instability after the cloud passes through the disk.

Key words: Galaxy: structure -- ISM: clouds -- ISM: individual: GW 123.4-1.5 -- ISM: structure

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