SINGS星系中高暗恒星形成区的出现
The Incidence of Highly-Obscured Star-Forming Regions in SINGS Galaxies
摘要：
利用斯皮策空间望远镜的新能力和斯皮策红外近星系巡天（SINGS）的大量多波长数据，现在有可能研究附近星系中恒星形成的红外特性，其尺度相当于大的HII区域。因此，我们能够确定正常星系中大的红外选择的恒星形成区域中有多少是高度模糊的，并解决我们仅仅依靠光谱的光学部分错过了多少恒星形成。采用一种新的经验方法推导红外选择性恒星形成区的衰减，我们调查了38个邻近星系样本中500 pc尺度的遮蔽恒星形成的统计数据。我们发现，在H-α的中值衰减是1.4个星等，并且没有证据表明存在大量均匀高度模糊的恒星形成区域。在衰减分布的高度模糊尾部（A_H-α> 3）的区域仅占近1800个区域样本的~4%，尽管在紧凑和超紧凑的HII区域中，几乎可以肯定存在更多的小得多的尺度和较低亮度的非常嵌入的红外源。在我们的样本中，高度模糊的情况通常是明亮的，具有高整体衰减的星系中心区域，但在其他方面并不显着。我们还发现，大多数星系的H-α衰减呈径向下降趋势。在这个正常的恒星形成星系样本中看到的一小部分高度模糊的区域表明，在500 pc尺度上，相对于典型恒星形成区域的寿命，附近光学厚度的尘埃云显着分散或破碎的时间尺度很短。
英文摘要：
Using the new capabilities of the Spitzer Space Telescope and extensive multiwavelength data from the Spitzer Infrared Nearby Galaxies Survey (SINGS), it is now possible to study the infrared properties of star formation in nearby galaxies down to scales equivalent to large HII regions. We are therefore able to determine what fraction of large, infrared-selected star-forming regions in normal galaxies are highly obscured and address how much of the star formation we miss by relying solely on the optical portion of the spectrum. Employing a new empirical method for deriving attenuations of infrared-selected star-forming regions we investigate the statistics of obscured star formation on 500pc scales in a sample of 38 nearby galaxies. We find that the median attenuation is 1.4 magnitudes in H-alpha and that there is no evidence for a substantial sub-population of uniformly highly-obscured star-forming regions. The regions in the highly-obscured tail of the attenuation distribution (A_H-alpha > 3) make up only ~4% of the sample of nearly 1800 regions, though very embedded infrared sources on the much smaller scales and lower luminosities of compact and ultracompact HII regions are almost certainly present in greater numbers. The highly-obscured cases in our sample are generally the bright, central regions of galaxies with high overall attenuation but are not otherwise remarkable. We also find that a majority of the galaxies show decreasing radial trends in H-alpha attenuation. The small fraction of highly-obscured regions seen in this sample of normal, star-forming galaxies suggests that on 500pc scales the timescale for significant dispersal or break up of nearby, optically-thick dust clouds is short relative to the lifetime of a typical star-forming region.
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