Vertical distribution of Galactic disc stars and gas constrained by a molecular cloud complex |
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| Authors: | Chanda J Jog Chaitra A Narayan |
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| Institution: | Department of Physics, Indian Institute of Science, Bangalore 560012, India |
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| Abstract: | We investigate the dynamical effects of a molecular cloud complex with a mass ～ 107 M⊙ and a size ～ a few 100 pc on the vertical distribution of stars and atomic hydrogen gas in a spiral galactic disc. Such massive complexes have now been observed in a number of spiral galaxies. The extended mass distribution in a complex, with an average mass density 6 times higher than the Oort limit, is shown to dominate the local gravitational field. This results in a significant redistribution or clustering of the surrounding disc components towards the mid-plane, with a resulting decrease in their vertical scaleheights.
The modified, self-consistent stellar density distribution is obtained by solving the combined Poisson equation and the force equation along the z -direction for an isothermal stellar disc on which the complex is imposed. The effect of the complex is strongest at its centre, where the stellar mid-plane density increases by a factor of 2.6 and the vertical scaleheight decreases by a factor of 3.4 compared with the undisturbed stellar disc. A surprising result is the large radial distance of ～ 500 pc from the complex centre over which the complex influences the disc; this is due to the extended mass distribution in a complex. The complex has a comparable effect on the vertical distribution of the atomic hydrogen gas in the galactic disc. This 'pinching' or constraining effect should be detectable in the nearby spiral galaxies, as for example has been done for NGC 2403 by Sicking. Thus the gravitational field of a complex results in local corrugations of the stellar and H i vertical scaleheights, and the galactic disc potential is highly non-uniform on scales of the intercomplex separation of ～ 1 kpc. |
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| Keywords: | ISM: clouds galaxies: ISM galaxies: kinematics and dynamics galaxies: spiral galaxies: structure |
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