paper

Extraplanar Dust in Spiral Galaxies: Observations and Implications

arXiv:astro-ph/9910092 · doi:10.1023/A:1017032610206

Abstract

Recent optical and submillimeter observations have begun to probe the existence of dust grains in the halos of spiral galaxies. I review our own work in this area which employs high-resolution optical images of edge-on spiral galaxies to trace high-z dust in absorption against the background stellar light of the galaxies. We have found that a substantial fraction of such galaxies (>50%) show extensive webs of dust-bearing clouds to heights z>2 kpc. Extraplanar dust in galaxies is statistically correlated with extraplanar diffuse ionized gas, though there is no evidence for a direct, physical relationship between these two phases of the high-z interstellar medium. The dense high-z clouds individually have masses estimated to be >10^5} to 10^6 solar masses. The detailed properties of the observed dust structures suggest the clouds seen in our images may represent the dense phase of a multiphase ISM at high-z. Such dense clouds can have an important effect on the observed light distribution in spiral galaxies. I discuss the effects such high-z dust can have on quantitative measures of the vertical structure of stars and ionized gas in edge-on systems.

To appear in "Toward a New Millennium in Galaxy Morphology," eds. D.L. Block, I. Puerari, A. Stockton, & D. Ferreira (Kluwer, Dordrecht). 8 pages; 3 embedded figures. Version with high-resolution figures available at http://fuse.pha.jhu.edu/~howk/Papers/papers.html

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