The Opacity of Spiral Galaxy Disks. IV. Radial Extinction Profiles from Counts of Distant Galaxies Seen through Foreground Disks
The Opacity of Spiral Galaxy Disks. IV. Radial Extinction Profiles from Counts of Distant Galaxies Seen through Foreground Disks
复制标题
螺旋星系盘的不透明度。
DOI：
10.1086/427716
复制
发表时间：
2004
期刊：
影响因子：
--
通讯作者：
P. Kruit
中科院分区：
文献类型：
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作者：
B. Holwerda;R. González;R. Allen;P. Kruit
尘埃的消失可以从通过螺旋盘看到的远场星系的数量来确定。为了校正前景图像带来的拥挤和混乱，González等人和Holwerda等人开发了合成场方法（SFM），该方法通过向候选前景星系场添加各种无遮挡背景场的深度曝光来分析合成场。SFM的优点是，它给出了星系盘区域的平均不透明度，而不需要假设吸收体的分布或星系盘星光的分布。然而，它受到现存场星系的统计数据的限制，因此需要结合更大的场样本。本文介绍了哈勃太空望远镜(HST)/WFPC2对29个螺旋星系的32个深层档案场样本的初步结果。本文给出了螺旋星系中基于远场星系校准计数的平均尘埃消光的径向分布，包括单个星系和来自我们样本的合成星系。讨论了倾角、旋臂和哈勃类型对径向消光剖面的影响。星盘的尘埃不透明明显地来自两个不同的组成部分：与旋臂相关的光学较厚（AI = 0.5 - 4等）但径向依赖的组成部分和相对恒定的光学较薄的盘（AI≈0.5等）。这些结果与早先对掩星系的研究完全一致。在我们的样品中，早期型的螺旋盘比后期的螺旋盘表现出更少的消光。表面亮度低的星系，可能还有Sd星系，看起来是透明的。通过前景盘看到的场星系的平均颜色似乎不随半径或不透明度而改变。这种灰色的行为很可能是由于不透明云的斑驳性质。径向环的平均消光和它的平均表面亮度似乎与较亮的区域相关。由此得出的结论是，螺旋盘上较亮的部分，如旋臂，也是与之相关的灭绝最多的部分。
Dust extinction can be determined from the number of distant field galaxies seen through a spiral disk. To calibrate this number for the crowding and confusion introduced by the foreground image, González et al. and Holwerda et al. developed the Synthetic Field Method (SFM), which analyzes synthetic fields constructed by adding various deep exposures of unobstructed background fields to the candidate foreground galaxy field. The advantage of the SFM is that it gives the average opacity for the area of a galaxy disk without making assumptions about either the distribution of absorbers or of the disk starlight. However, it is limited by poor statistics on the surviving field galaxies, hence the need to combine a larger sample of fields. This paper presents the first results for a sample of 32 deep Hubble Space Telescope (HST)/WFPC2 archival fields of 29 spiral galaxies. The radial profiles of average dust extinction in spiral galaxies based on calibrated counts of distant field galaxies is presented here, both for individual galaxies and for composites from our sample. The effects of inclination, spiral arms, and Hubble type on the radial extinction profile are discussed. The dust opacity of the disk apparently arises from two distinct components: an optically thicker (AI = 0.5–4 mag) but radially dependent component associated with the spiral arms and a relatively constant optically thinner disk (AI ≈ 0.5 mag). These results are in complete agreement with earlier work on occulted galaxies. The early-type spiral disks in our sample show less extinction than the later types. Low surface brightness galaxies, and possibly Sd's, appear effectively transparent. The average color of the field galaxies seen through foreground disks does not appear to change with radius or opacity. This gray behavior is most likely due to the patchy nature of opaque clouds. The average extinction of a radial annulus and its average surface brightness seem to correlate for the brighter regions. This leads to the conclusion that the brighter parts of the spiral disk, such as spiral arms, are also the ones with the most extinction associated with them.