揭开尘埃面纱II：银河系红外消光定律的大尺度研究
Lifting the Dusty Veil II: A Large-Scale Study of the Galactic Infrared Extinction Law
摘要：
我们结合近红外（2 MASS）和中红外（斯皮策-IRAC）测光的特点红外消光定律（1.2-8微米）超过近150度的连续银河系中面经度。通过计算G和K巨红团簇星在相邻中面区域的色过剩比，并推导出每个区域的消光系数与波长的关系，得到了这些波长和经度范围内5个通带的相对消光系数。消光定律形状的强烈单调变化被发现是与银河系中心的角度的函数，在银河系中心的两侧对称。这些纵向变化持续存在，即使在稠密的星际区域，先验已知有一个较浅的消光曲线，被删除。越往外越陡的消光曲线表明，在较大的银心角下，绝对消光比和选择消光比（RV）以及尘埃平均粒径都在稳步减小。我们注意到，在高银心角的8微米消光拐点的强度增加，并使用理论尘埃模型，表明这种行为是一致的趋势，在R_V。沿着几条视线的解决方案是最可行的，A_lambda/A_Ks作为银河系半径的函数估计，并显示有一个银河系的径向依赖。我们的分析表明，所观察到的消光曲线形状和银河经度之间的关系是由于内在的依赖关系的消光定律银心半径。
英文摘要：
We combine near-infrared (2MASS) and mid-infrared (Spitzer-IRAC) photometry to characterize the IR extinction law (1.2-8 microns) over nearly 150 degrees of contiguous Milky Way midplane longitude. The relative extinctions in 5 passbands across these wavelength and longitude ranges are derived by calculating color excess ratios for G and K giant red clump stars in contiguous midplane regions and deriving the wavelength dependence of extinction in each one. Strong, monotonic variations in the extinction law shape are found as a function of angle from the Galactic center, symmetric on either side of it. These longitudinal variations persist even when dense interstellar regions, known a priori to have a shallower extinction curve, are removed. The increasingly steep extinction curves towards the outer Galaxy indicate a steady decrease in the absolute-to-selective extinction ratio (R_V) and in the mean dust grain size at greater Galactocentric angles. We note an increasing strength of the 8 micron extinction inflection at high Galactocentric angles and, using theoretical dust models, show that this behavior is consistent with the trend in R_V. Along several lines of sight where the solution is most feasible, A_lambda/A_Ks as a function of Galactic radius is estimated and shown to have a Galactic radial dependence. Our analyses suggest that the observed relationship between extinction curve shape and Galactic longitude is due to an intrinsic dependence of the extinction law on Galactocentric radius.
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