Gaps in the cloud cover? Comparing extinction measures in spiral disks
| Autor: | Holwerda, B. W., Meyer, M., Regan, M., Calzetti, D., Gordon, K. D., Smith, J. D., Dale, D., Engelbracht, C. W., Jarrett, T., Thornley, M., Bot, C., Buckalew, B., Kennicutt, R. C., Gonzalez, R. A. |
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| Rok vydání: | 2007 |
| Předmět: | |
| Zdroj: | Astron.J.134:1655-1661,2007 |
| Druh dokumentu: | Working Paper |
| DOI: | 10.1086/521824 |
| Popis: | Dust in galaxies can be mapped by either the FIR/sub-mm emission, the optical or infrared reddening of starlight, or the extinction of a known background source. We compare two dust extinction measurements for a set of fifteen sections in thirteen nearby galaxies, to determine the scale of the dusty ISM responsible for disk opacity: one using stellar reddening and the other a known background source. In our earlier papers, we presented extinction measurements of 29 galaxies, based on calibrated counts of distant background objects identified though foreground disks in HST/WFPC2 images. For the 13 galaxies that overlap with the Spitzer Infrared Nearby Galaxies Survey (SINGS), we now compare these results with those obtained from an I-L color map. Our goal is to determine whether or not a detected distant galaxy indicates a gap in the dusty ISM, and hence to better understand the nature and geometry of the disk extinction. We find that distant galaxies are predominantly in low-extinction sections marked by the color maps, indicating that their number depends both on the cloud cover of {\it Spitzer}-resolved dust structures --mostly the spiral arms--and a diffuse, unresolved underlying disk. We note that our infrared color map (E[I-L]) underestimates the overall dust presence in these disks severely, because it implicitly assumes the presence of a dust screen in front of the stellar distribution. Comment: 22 pages, 2 figures, 3 tables, accepted for publication in AJ |
| Databáze: | arXiv |
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