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arXiv 1702.06006astro-ph.GA
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在大螺旋设计图NGC1566上的恒星形成层次

Hierarchical star formation across the grand design spiral NGC1566

Dimitrios A. Gouliermis, Bruce G. Elmegreen, Debra M. Elmegreen, Daniela Calzetti, Michele Cignoni, John S. Gallagher, Robert C. Kennicutt, Ralf S. Klessen, Ele… 展开作者

Dimitrios A. Gouliermis, Bruce G. Elmegreen, Debra M. Elmegreen, Daniela Calzetti, Michele Cignoni, John S. Gallagher, Robert C. Kennicutt, Ralf S. Klessen, Elena Sabbi, David Thilker, Leonardo Ubeda, Alessandra Aloisi, Angela Adamo, David O. Cook, Daniel Dale, Kathryn Grasha, Eva K. Grebel, Kelsey E. Johnson, Elena Sacchi, Fayezeh Shabani, Linda J. Smith, Aida Wofford

摘要:

我们调查如何恒星形成的空间组织在大设计的螺旋NGC 1566从深HST测光与遗产银河系外紫外线调查(LEGUS)。我们基于等高线的聚类分析揭示了890个不同级别的显著性恒星聚集体。这些恒星形成的复合体以等级的方式组织起来,较大的聚集体由较小的结构组成,它们本身又分裂成更小、更紧凑的恒星群。它们的尺寸分布,覆盖了很宽的长度尺度范围,表现出幂律预期的无标度过程。我们用一个简单的“碎片化和富集”模型解释了这种形状。的复合物的层次形态证实了它们的质量-尺寸的关系,可以表示为幂律与分数指数,类似于分形分子云确定。复合体的表面恒星密度分布呈对数正态分布,类似于超音速非重力湍流气体的分布。50%至65%的新近形成的恒星,以及大约90%的年轻星团,都位于螺旋臂上的恒星复合体内部。我们发现复合体内部的年轻恒星和它们附近的恒星之间的年龄差至少为1000万年。这个时间尺度可能与恒星蒸发的最短时间有关,尽管我们不能排除恒星的原位形成。正如预期的那样,恒星的形成优先发生在旋臂中。我们的发现揭示了顺磁驱动的分层恒星形成沿着一个宏伟的设计星系的手臂。

英文摘要:

We investigate how star formation is spatially organized in the grand-design spiral NGC 1566 from deep HST photometry with the Legacy ExtraGalactic UV Survey (LEGUS). Our contour-based clustering analysis reveals 890 distinct stellar conglomerations at various levels of significance. These star-forming complexes are organized in a hierarchical fashion with the larger congregations consisting of smaller structures, which themselves fragment into even smaller and more compact stellar groupings. Their size distribution, covering a wide range in length-scales, shows a power-law as expected from scale-free processes. We explain this shape with a simple "fragmentation and enrichment" model. The hierarchical morphology of the complexes is confirmed by their mass--size relation which can be represented by a power-law with a fractional exponent, analogous to that determined for fractal molecular clouds. The surface stellar density distribution of the complexes shows a log-normal shape similar to that for supersonic non-gravitating turbulent gas. Between 50 and 65 per cent of the recently-formed stars, as well as about 90 per cent of the young star clusters, are found inside the stellar complexes, located along the spiral arms. We find an age-difference between young stars inside the complexes and those in their direct vicinity in the arms of at least 10 Myr. This timescale may relate to the minimum time for stellar evaporation, although we cannot exclude the in situ formation of stars. As expected, star formation preferentially occurs in spiral arms. Our findings reveal turbulent-driven hierarchical star formation along the arms of a grand-design galaxy.

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