解构星系：Messier 83中点源的颜色分布
Deconstructing a galaxy: colour distributions of point sources in Messier 83
摘要：
当我们观察附近清晰的星系时，我们看到了什么？在对附近星系的一小部分进行多波段成像观测时，可以探测到数千个单独的源，而表征这些源是一个复杂的过程。这项工作分析了附近螺旋星系Messier 83的7.3平方弧分区域中近70，000个点源的十波段测光目录，作为早期发布科学计划的一部分，哈勃太空望远镜的宽视场相机3。测量了宽带和宽窄带颜色的颜色分布;由具有大波长差的宽带制成的颜色通常具有更宽的分布，尽管B-V是个例外。使用四个波段的各种组合生成二维和三维颜色空间，并使用K-Means和Mean Shift算法进行聚类。这两种算法都不能一致地分割颜色分布：虽然颜色空间中的一些独特特征在视觉检查中很明显，但这些特征不够紧凑或孤立，无法被识别为颜色空间中的聚类。UBVI颜色空间的K均值聚类能够识别出一组更可能是星团的物体。均值偏移法成功地识别了颜色分布边缘的离群组。对于识别发射以谱线为主的物体，与简单的连续谱减法相比，在多个波段结合窄带光度测定没有明显的好处。聚类分析结果用于为未来对附近星系的调查提供建议。
英文摘要：
What do we see when we look at a nearby, well-resolved galaxy? Thousands of individual sources are detected in multiband imaging observations of even a fraction of a nearby galaxy, and characterizing those sources is a complex process. This work analyses a ten-band photometric catalogue of nearly 70 000 point sources in a 7.3 square arcmin region of the nearby spiral galaxy Messier 83, made as part of the Early Release Science programme with the Hubble Space Telescope's Wide Field Camera 3. Colour distributions were measured for both broad-band and broad-and-narrow-band colours; colours made from broad-bands with large wavelength differences generally had broader distributions although B - V was an exception. Two- and three-dimensional colour spaces were generated using various combinations of four bands and clustered with the K-Means and Mean Shift algorithms. Neither algorithm was able to consistently segment the colour distributions: while some distinct features in colour space were apparent in visual examinations, these features were not compact or isolated enough to be recognized as clusters in colour space. K-Means clustering of the UBVI colour space was able to identify a group of objects more likely to be star clusters. Mean Shift was successful in identifying outlying groups at the edges of colour distributions. For identifying objects whose emission is dominated by spectral lines, there was no clear benefit from combining narrow-band photometry in multiple bands compared to a simple continuum subtraction. The clustering analysis results are used to inform recommendations for future surveys of nearby galaxies.
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