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Session 75 - Dust & PAHs in Galaxies.
Display session, Friday, January 09
Exhibit Hall,

[75.01] HST and ISO Mapping of Dust in Silhouetted Spiral Galaxies

W. C. Keel, R. E. White III (U. Alabama)

We present first results of an HST and ISO program to determine the fine-scale distribution of dust in spirals. We use neighboring early-type galaxies as background light sources to measure dust extinction in the HST data. We contrast the cases of two spirals projected in front of E/S0 galaxies, AM1316-241 and AM0500-620, from B and I WFPC2 images. In the outer arms, we find no regions with \tau_B > 1.5 even at a typical resolution of 50 pc. AM0500-620 shows dust lanes associated with interarm spurs, while there is essentially no interarm dust seen in AM1316-241. The arm dust in AM0500-620 is strongly concentrated to rather thin narrow lanes, extending at least as far out as the optically detected arms do, while the dust distribution in AM1316-241 is broad and strongly textured. Within the dust arms of AM0500-620, we find some features which differ substantially in spatially averaged selective-to-total extinction, which suggests that the dust clumping and averaged column density may sometimes be decoupled.

ISOCAM images at 17\mu are available for AM1316-241, in which the strong backlit dust lane is undetected as a warm dust source (though we do expect it as a statistical contributor to the overall 50-100\mu ISOPHOT maps). In an additional pair, AM1318-432=NGC 5090/1, the strong backlit dust lane is detected as a mid-IR source, signifying embedded star formation. When far-IR ISOPHOT data are added, we expect to derive significant constraints on the entire spatial spectrum of dust clumping.

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