旋涡星系中的扩展尘埃盘; ANGST中的一对掩星星系
An extended dust disk in a spiral galaxy; An occulting galaxy pair in ANGST
摘要：
我们提出了一个掩星星系对的分析，偶然发现在ACS附近的星系调查金库（ANGST）的NGC 253的观测与哈勃太空望远镜的先进相机调查在F475 W，F606 W $和F814 W（SDSS-g，宽V和I）。前景盘系统（z < 0.06）显示了一个比星光更长的尘埃盘，在消光中看到的螺旋线达到1.5 R25，大约是六个半光半径。这对是第一个可以可靠地将消光映射到距离中心的距离的地方。扩展尘埃盘的旋臂显示出典型的消光值A_F475W ~ 0.25，A_F606W ~ 0.25，A_F814W ~ 0.15.从这些措施推断的消光定律是类似的本地银河系之一，我们表明，在有限的空间分辨率（<57 pc，在这些数据中）采样的平滑效果，通过混合不同的消光区域的观察功能。这个星系说明了螺旋星系中尘埃分布的多样性，以及对光学相似星系采用单一尘埃模型的局限性。这对重叠星系的理想几何形状和HST数据的高采样使得该数据集非常适合用三种不同的方法来分析这对重叠星系：（A）组合拟合，旋转两个星系的副本，（B）背景图像的简单翻转和（C）基于重建其适当的等照度线来估计单个星系的原始通量。我们的结论是，在高质量的数据，如这些情况下，等照度线模型是首选。
英文摘要：
We present an analysis of an occulting galaxy pair, serendipitously discovered in ACS Nearby Galaxy Survey Treasury (ANGST) observations of NGC 253 taken with Hubble Space Telescope's Advanced Camera for Survey in F475W, F606W$ and F814W (SDSS-g, broad V and I). The foreground disk system (at z < 0.06) shows a dusty disk much more extended than the starlight, with spiral lanes seen in extinction out to 1.5 R\_25, approximately six half-light radii. This pair is the first where extinction can be mapped reliably out to this distance from the center. The spiral arms of the extended dust disk show typical extinction values of A\_F475W ~ 0.25, A\_F606W ~ 0.25, and A\_F814W ~ 0.15. The extinction law inferred from these measures is similar to the local Milky Way one, and we show that the smoothing effects of sampling at limited spatial resolution (<57 pc, in these data) flattens the observed function through mixing of regions with different extinction. This galaxy illustrates the diversity of dust distributions in spirals, and the limitations of adopting a single dust model for optically similar galaxies. The ideal geometry of this pair of overlapping galaxies and the high sampling of HST data make this dataset ideal to analyze this pair with three separate approaches to overlapping galaxies: (A) a combined fit, rotating copies of both galaxies, (B) a simple flip of the background image and (C) an estimate of the original fluxes for the individual galaxies based on reconstructions of their proper isophotes. We conclude that in the case of high quality data such as these, isophotal models are to be preferred.
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