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Session 75 - Dust & PAHs in Galaxies.
Display session, Friday, January 09
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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Program listing for Friday