Other
Scientific paper
Dec 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phdt........11h&link_type=abstract
Thesis (PhD). THE UNIVERSITY OF WISCONSIN - MADISON, Source DAI-B 60/06, p. 2747, Dec 1999, 213 pages.
Other
Interstellar Media
Scientific paper
This work presents observations of edge-on spiral galaxies using the WIYN 3.5-m observatory on Kitt Peak designed to dust in the disk-halo interface of spirals. High-resolution ( 0.'' 6 - 0.'' 8 ) broadband BVRI and narrowband Ha images of the edge-on Sb galaxy NGC 891. These images reveal a complex network of hundreds of dust absorbing structures far from the mid- plane of the galaxy, visible to |z|>~ 2.5 kpc from the midplane. However, the number and attenuation of highly-structured (clumped) dust clouds is significantly lesser at heights in excess of z ~ 1.7-2.0 kpc than at lower z. These high- z dusty clouds are estimated to have gas column densities NH >~ 1021 cm-2, with in excess of 10 5 Msolar , and gravitational potential energies > 1052 ergs, assuming Galactic gas-to-dust relationships. The Hα data presented herein show a lack of small-scale correspondence between the dust features visible in the BVRI images and extraplanar ionized gas. An imaging survey of 12 nearby edge-on spirals shows extraplanar dust like that observed in NGC 891 is a common feature of spiral galaxies. In a statistical sample of seven massive L*- like spiral galaxies within D <~ 25 Mpc that have inclinations i >~ 87° from the plane of the sky, five of these systems show extraplanar dust. All of the galaxies in our sample that show detectable Hα emission at large z also show extraplanar dust structures. None of those galaxies for which extraplanar Hα searches were negative show evidence for extensive high- z dust. The dust-bearing clouds revealed in our broadband images likely represent a dense phase of the ISM in the interstellar thick disk of NGC 891 and other galaxies, physically distinct from the ionized phase of the high- z ISM. All of the phases of the interstellar medium observed in the disk of the Milky Way are also present in the extended thick disks, or halos, of spiral galaxies. The existence of the dense, extraplanar dust structures seen in our images is dictated by the pressure of the high-z interstellar medium.
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