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Session 75 - Dust & PAHs in Galaxies.
Display session, Friday, January 09
Exhibit Hall,
Using archival WFPC2 images, we develop and apply a method of using dust as a tracer of ongoing disk-halo interactions (DHIs) in edge-on galaxies. The initial goal is to prove that dust exists in the halos of galaxies ONLY when the star formation (SF) rate (and thereby the FIR luminosity) is high. To accomplish this requires differentiating between thin dust disks, thick dust disks, and halo dust. Thin dust disks are typical of galaxies with low SF rates while thick disks can be found in dynamically hot systems, like e.g. S0 galaxies. Our preliminary analysis has revealed that dust disks can be distinguished from disk+halo dust via the slope of averaged z-slices. While the disks, be they thin or thick, cut off sharply with increasing z, the existence of halo dust (expelled by high-level SF) produces z-profiles with shallower gradients. The technique employed is similar to that used to trace radio continuum halos, however dust absorption measurements are several orders of magnitude more sensitive, because they depend only on the presence of background stellar light. The bias that early-type galaxies have more such background light than late types works in our favor, since SF-related gaseous halos are expected to exist only in galaxies of type Sb or later (Kennicutt, Edgar, Hodge 1989, ApJ). We present here a subset of targets as a progress report on the method and results.
