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B. W. Holwerda (STScI), R. A. Gonzalez (UNAM), R. J. Allen, D. Calzetti (STScI), P. C. van der Kruit (Kapteyn Astronomical Institute), SINGS Team
Dust emission in the far-infrared (FIR) characterizes the temperature and quantity of interstellar dust in a spiral disk. The three Spitzer/MIPS bands are well suited to measuring the gradient in temperature and the total optical depth in the disk of a spiral galaxy.
Another way to estimate the quantity of dust in a spiral disk is the "Synthetic Field Method" (SFM), which uses the number of distant field galaxies seen through the disk of the nearby spiral. The optical depth estimated from this method can be compared to the values derived from the FIR emission. Since the two techniques depend on different assumptions regarding the dust cloud cover, clumpiness, and emissivity, this comparison between the optical depth profiles can shed light on the structure and quantity of the ISM in spiral disks, especially any colder components.
Here we present the comparison between the radial opacity profiles for galaxies as derived using the SFM, and as derived from Sptizer/MIPS observations. The dust responsible for the opacity from distant galaxy counts appears to be predominantly cold (T \approx 20 K.). The MIPS observations were part of the Spitzer Infrared Nearby Galaxies Survey (SINGS).
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.