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The infrared extinction law in various interstellar environments. Shu Wang 11, 30, 2012 Beijing Normal University Email: shuwang @ mail.bnu.edu.cn. Outline. Background Data Selected typical environments Method Tracers Selection Result and Discuss relative extinction A λ /A ks
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Shu Wang 11, 30, 2012
Beijing Normal University
Our work: whether the IR extinction law relates to the interstellar environment or not and how it relates
[3.6], [4.5], [5.8] and [8.0] μm
visual extinction is Av, the dust column density is N, the dust volume density is n, the distance of the sight line is L
AV large region: orange
AVtransition region: green
Fig. 1.— A sample extinction map of the Coalsack by Dobashi et al. (2005). The resolution of the map is 6′.
Fig. 2.— The Spitzer 8.0 μm image of a part of the Coalsack around l = 305.5°. The resolution of the image mosaics is 1.2 arcsec per pixel. The black filaments are due to dust emission, specially the PAH emission. The selected 8 μm emission region is marked with violet box.
Fig. 3.— Map of the velocity integrated CO (1-0) emission of Coalsack (Nyman et al. 1989).
Fig. 4.— The MSX 8.3 μm image of a part around l = 28°. The IRDCs and cores identified by Simon et al. (2006) are marked with black ellipses and white ellipses respectively. The cloud G028.23-00.19 marked with blue ellipse is shown on the image.
Fig. 5.— J-Ks vs. J diagram for the 8 μm emission region in Table 1. The black dots are all the sources for the field of the GLIMPSE I which contains the 8 μm emission region and red crosses are the selected red giants for the 8 μm emission region.
Fig. 6.— The 2MASS and IRAC color-color diagrams for the sources in Figure 5. The green lines are the best fits to the data. The blue points are dropped by a 3σcriterion.
Fig. 7.— Comparing sub-regions value with each other, the diffuse (1) region has the highest relative extinction and the 8 μm emission region has the lowest value. It is well consistent with the experience: the relative extinction in diffuse region is higher and in dense region is lower in four IRAC bands. It may be explained by the theory of dust growth in dense region.
Fig. 8.— Comparing the mean extinction with previous results and the extinction curves calculated from the interstellar grain model for Rv = 3.1 (solid line) and for Rv = 5.5 (dot-dashed line) by Weingartner & Draine (2001). It is found all the regions have flat mid-IR extinction curve which are consistent with the modeled extinction curve of Rv =5.5.