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Session 2 - Spiral, Irregular and Elliptical Galaxies.
Display session, Monday, June 09
South Main Hall,

[2.03] WIYN Imaging of Extraplanar Dust in the Edge-On Spiral NGC 891

J. C. Howk, B. D. Savage (U. Wisconsin)

We present high-resolution (0.50-0.65'') broad-band BVR optical images of the edge-on Sb galaxy NGC 891 taken with the WIYN 3.5-m telescope. Numerous dust extinction features can be seen against the background stellar light; many of these dust features can easily be traced to 1.5 kpc from the galaxy midplane. The images unambiguously reveal numerous and complex dust structures at significant z-distances from the thin interstellar disk of NGC 891.

We discuss the sizes and morphologies of several individual extinction complexes whose lengths range from 100-600 pc (though these structures may be superpositions of several features along the line-of-sight). Taken as an ensemble, the absorbing properties of the dust features in the BVR bands are consistent with Galactic-like dust absorption. Assuming Galactic dust-to-gas ratios we derive approximate hydrogen column densities for several individual complexes using the apparent extinctions in the BVR images. The derived hydrogen column densities are generally of order 10^21 atoms cm^-2, suggesting these structures contain significant amounts of interstellar material.

Several of the identified features are clearly associated with the very active star-formation in the disk on the NE side of the galaxy. Other features are not as readily identified with star-formation activity. It is not yet clear what is causing these latter features.

These images represent the beginning of a larger project to study off-plane dust structures and their relationship to ionized gas structures in highly-inclined spirals with the WIYN telescope. The goal of this project is to study the interstellar disk-halo interface in spirals and the role that dust plays in this interface.

Program listing for Monday