THE MID-INFRARED EXTINCTION LAW IN THE OPHIUCHUS, PERSEUS, AND SERPENS MOLECULAR CLOUDS
- Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
- Institute of Astronomy and Department of Physics, National Tsing Hua University, Hsinchu 30043, Taiwan (China)
- Department of Astronomy, University of Texas at Austin, 1 University Station C1400, Austin, TX 78712 (United States)
We compute the mid-IR extinction law from 3.6 to 24 {mu}m in three molecular clouds-Ophiuchus, Perseus, and Serpens-by combining data from the 'Cores to Disks' Spitzer Legacy Science program with deep JHK{sub s} imaging. Using a new technique, we are able to calculate the line-of-sight (LOS) extinction law toward each background star in our fields. With these LOS measurements, we create, for the first time, maps of the {chi}{sup 2} deviation of the data from two extinction law models. Because our {chi}{sup 2} maps have the same spatial resolution as our extinction maps, we can directly observe the changing extinction law as a function of the total column density. In the Spitzer Infrared Array Camera (IRAC) bands, 3.6-8 {mu}m, we see evidence for grain growth. Below A{sub K{sub s}}= 0.5, our extinction law is well fitted by the Weingartner and Draine R{sub V} = 3.1 diffuse interstellar-medium dust model. As the extinction increases, our law gradually flattens, and for A{sub K{sub s}}{>=}1, the data are more consistent with the Weingartner and Draine R{sub V} = 5.5 model that uses larger maximum dust grain sizes. At 24 {mu}m, our extinction law is 2-4 times higher than the values predicted by theoretical dust models, but is more consistent with the observational results of Flaherty et al. Finally, from our {chi}{sup 2} maps we identify a region in Perseus where the IRAC extinction law is anomalously high considering its column density. A steeper near-IR extinction law than the one we have assumed may partially explain the IRAC extinction law in this region.
- OSTI ID:
- 21565478
- Journal Information:
- Astrophysical Journal, Vol. 690, Issue 1; Other Information: DOI: 10.1088/0004-637X/690/1/496; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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